Compared to its predecessors, Sam II comes with both better and worse qualities... more good than bad news, however.
Trying to recreate that feel, Croteam 2005's Serious Sam II comes with both better and worse qualities. While the updated engine (Serious Engine 2) looks great, it isn't possible to render lots of enemies and those huge levels without lagging. The result is a game with more linear levels, filled with less monsters and detail. Nevertheless, Serious Sam stills an old-school FPS, and just because instead having 1000 monsters the player will actually get 500 per level, it doesn't mean the game is bad. It still have a lot of fun secrets (some important, while others are just cool) and several areas with literally dozens of monsters, all mindlessly attacking Sam Stone at the same time.
Most weapons were recycled from the original Serious Sam games: The Double-Barreled Shotgun, the Minigun, the Rocket Launcher, the Grenade Launcher, the Sniper Rifle, the amazing Cannon, the 'problem solver' Serious Bomb etc. And there're new ones too: Klodovic (a parrot that carries a powerful explosive), a sort of an energy pistol (I found it a rip-off from Unreal II's Dispersion Pistol), a plasma gun, which is as powerful as the Laser Gun from the original Serious Sam. All of these weapons are useful against certain types of enemies. You'll prefer to use the Sniper Rifle to take down ranged enemies at distance, while the Double-Barreled Shotgun is amazing in close combats.
Serious Sam II delivers some good action sequences, although it isn't as tactical as the first two games. I mean, in both 'The First' and 'The Second Encounter' the player needs to pay attention to the sounds that most monsters have. If you hear a scream, then you know that the beheaded kamikaze is near (almost exploding you). Or if it's a galloping sound that you noticed, then stay alert because a Kleer skeleton must be nearby, if it's not already attacking you. Those things don't make sense anymore in Serious Sam II. Additionally, most of your weapons work perfectly fine in almost all the situations. The shotgun can fire with extremely precision, no matter the distance in question. This makes Serious Sam II a bit easy, even at 'Normal' difficult. The dual pistols are another problem: they're pretty weak, and I can easily include in that category the energy pistol (I didn't use it a single time in the whole game) and the chainsaw, which was very useful in 'The Secound Encounter'.
Now, differently from many reviewers here in Gamespot, I found the monsters and the levels amazing in this sequel. The game is much bigger now (nearly 40 levels), the environments aren't never the same, and there're a good variety of monsters, although most of them are repeated over the time. Some enemies are just remakes from the original Serious Sam, such as the bull, the beheaded kamikaze, the orc soldiers and the galloping skeleton; while others are completely new to the series: the suicide clown, the helicopters (as well much other flying things), the towers and so.
The levels are divided in seven episodes (or worlds), each one with an unique look, as well some few monsters that you'll see only in that particular world. Some levels are cartoony, while others are so well-done that even beat the quality even of most great games, such as DOOM 3 or Quake 4. The Kleer world, in my opinion, is exactly how DOOM 3 should look like in most of the time (instead of that indoor environment in the UAC facility), Also, the Sirious world is one of the most well-designed scenario ever in a PC game. The levels still big, although they don't have those big arenas as the ones in 'The First' and 'Secound Encounter'. While Serious Sam II is surely a lengthy game, it doesn't mean it will consume all of your free time. I managed to finish the game in less than 10 hours playing at 'Normal' difficult. Of course, if you decide to search for all the secrets, you'll spend several additional hours to do the job.
If the sound isn't as good (or useful) as it were in the original Serious Sam, at least the music still good in most of the levels. Yes, there're a few exceptions where the soundtrack is terrible, and will annoy the player in just a few minutes (luckily you can turn it off anytime you want). However, the weapons sound good, especially the Sniper, the Cannon and the plasma gun; also, the parrot Klodovic is really funny.
Talking about fun, this game is filled with good humor. Unfortunately, it has some false attempts of humor, making the game silly (not in the fun way). The cut scenes are mostly really cool, but sometimes they're stupid and you'll want to skip them in no time. Also, the NETRICSA, a system that lives in Sam's head giving all the information you need, isn't as useful as it was before. It still important to read the info, but doesn't have all that cool stuff about monsters behavior, local story and weapon strategy tips.
The Multiplayer is still there, especially the excellent Cooperative mode (up to 16 players). The bad news is that you'll need to apply the official patch (v2.070) to add the Deatchmatch mode. But playing with friends against Mental hordes is the real deal, the boss battles becomes even more interesting in that way.
So, considering everything that is new and really good, you can easily forgive the flaws present in Serious Sam II. An old-school FPS game with good Multiplayer, great graphics, lengthy campaign, generally funny moments and unique arcade gameplay cannot be so hated, or receive bad reviews just because isn't equal to its antecessors. There're good features that shines over all its problems.