Halo Wars is an accessible experience for those new to the genre, while maintaining enough depth to keep it interesting.
Set 20 years before the events of Halo, the Covenant have discovered a reilc on Harvest, and the UNSC need to find out what they are up to. The man for the job is Sargeant Forge, who you will play as for most of the campaign. Sometimes you will have Forge as an infantry unit, though most times he will be as an upgraded Warthog. The story is told through excellent cut scenes, with believable characters, and it is those characters that often give you a reason for continuing your campaign. Certain plotlines might be predictable, but they are still effective.
You are eased into gameplay with two optional tutorials which tell you most of what you need to get started. The missions themselves start out quite easy, with no base building in your first mission, and some hand holding in your next few missions (can't build some items until you have built a pre-requisite building) but after that the reins are free and you can start building everything available in the game. Base building and resources is an interesting model; bases can only be built in pre-determined locations, and each base has 'building slots' and you can only build a limited number of buildings at each base. Bases can be upgraded to a total of 8 additional buildings, but if your base gets destroyed, all the building go as well. Supply pads are one of those buildings; you don't need to collect any resources from the environment, but there are a few crates lying about the place, and collecting these early will often accelerate your growth.
You could say the limited building spaces dictates your strategy, or vice versa you could say your strategy dictates which buildings you need. Building extra supply pads means more resources, but then you have less space for diversity of other buildings. To upgrade your tech level you also need reactors, so getting the most powerful units or upgrades means you need at least 2 reactor spaces (as each can be upgraded to provide 2 tech levels). That said you can often take over another base halfway through a mission to provide you that extra diversity you may not have in your initial base.
To take over those bases, you are going to need units, and you are provided a range of different troops to help you achieve that goal. The Halo universe comes alive in the units, and it feels fully realised. From regular troops, to Scorpions, Warthogs and Hornets, virtually everything from previous Halo games is here and fits perfectly. All units have various upgrades that can be applied at the place they are built. While some of these are passive, most are special abilities that can be activated once the units are selected. For example, Wolverines are good at anti-air, but with an upgrade they can unleash a missile shot that is devastating to buildings or ground units. Once activated, it then takes time to charge up again before you can activate it again. Spartans can also be on the scene, but these are provided to you during missions, and you can't train them. On the plus side, Forge and any Spartans can not be totally killed in combat; if they are defeated, they will remain on the battlefield until their health slowly restores to half, and sending another unit nearby will revive them. Spartans can also hop into vehicles to really increase their combat ability... or jump onto enemy vehicles and steal them. You may also find cover available on most missions, and infantry who are garissoned in cover, Spartan or otherwise, are extremely effective.
Whether as a result of hardware limitations or just the intention to keep battles small, there is a relatively low population limit of 30, which you can increase to 40 with an upgrade. Further to this, more powerful units can take up more than one space of the population, so you can't just spam 40 of the most powerful units if you are resource heavy. However this doesn't really feel out of place in the scheme of things. It keeps things moving, because if you have reached your population limit, it compels you into combat, and the low population limit means you are more effectively able to manage units special abilities. The Covenant are your main enemies who have the troops and vehicles you would expect from experience with previous Halo games. Suffice to say you will pee your pants when you encounter your first Scarab. The Flood also appear a little later in the campaign, though only a few missions have you directly attacking a major Flood enemy. Differently to the Covenant, their spawning grounds eventually regenerate, meaning keeping troops on hand to take them out periodically to prevent a build up of their troops.
The missions themselves are quite varied. You will defend ships as they evacuate civilians, remove Flood from the hull of the Spirit of Fire as a 'ring' periodically cleanses it (destroying defeated Flood while damaging your units if they are in its path), and rescuing troops who are stranded on the far side of a map. Perhaps my favourite is coming across a prototype Scarab, and a beam of light keeps scanning from the top of the map; any units in its way it will lock on to and destroy. Most missions also have one or more optional objectives. For some of the missions it's as simple as killing a certain number of a certain type of enemy, but others might include setting up a second base, or destroying a certain number of pillars with electro-magnetic pulses. These give the game some replay value once you know the map, as these tie in to the medal system. Often I'm not compelled to replay games, but I went ahead and went back to get all the gold medals for this game because I enjoyed it so much.
That's not to say that Halo Wars doesn't have some flaws. The camera is focused in quite tightly, and while you have options to zoom in and out, it still doesn't feel like it zooms out far enough to get a better handle of things. While there are a few 'hotkeys', you can't assign units to squads to recall at a later time. You can select all units on the screen, or all units on the map, and then cycle through those if you want to hone it down to a particular unit type. Due to the smaller scale of battles this serves reasonably well, but limits your options somewhat without having to scan the screen to select indivudual units, or if you want a squad of mixed units. While I only played on the Medium setting and perhaps should have cranked it up to Heroic, it did seem a little on the easy side. While the cutscenes are excellent in their production values, the in-game graphics are a little underwhelming, but it doesn't distract and everything is easily identifiable as from the Halo universe.
But still, I think these flaws aside Halo Wars was designed to be an accessible game and in this respect it has succeeded with flying colours. The missions in the campaign aren't elongated battles that take hours to complete, making it easier to digest in bite-size chunks, but on the flipside it makes the campaign a little short in that it only has 15 missions. Being able to play afterwards as the Covenant would have been welcomed to extend the gameplay. Even so, there is some extra replay value in obtaining gold medals for each mission, finding hidden crates and skulls (which can modify gameplay settings for missions), and playing skirmish either against the AI or via Xbox Live. While I have not tested the live multiplayer as it generally does not appeal to me, this then gives you the option of playing as the Covenant, and each side allows you to choose from 3 different commanders, which award you different bonuses on the field. Audio is excellent and keeps you informed as to what is going on and where. PC real time strategy veterans might be turned away by the lack of some options and features, but anyone who has a passing interest or wants to get their feet wet in what can be a daunting genre, I recommend giving Halo Wars a go.