Bioware delivers a good game with issues that cannot be overlooked
The story is well told, and it really does feel like every decision you make changes the direction that the game is going in. The AI of you squad seems to be pretty solid, although controlling them is not really a fun experience. It seems to be much more practical to just let them do what they will, and focus on you own character. There are some issues at times with opponent AI, however. They often just foolishly rush straight at you, but also tend to just lounge around. Even with this AI issue, it's still quite easy to get immersed into what is going on. There were several times where I was surprised at how engaging the story is.
There are plenty of side quests, but the actual story line can be as short as 13 hours. The side quests are generally enjoyable, but planets tend to all be the same. Some are bumpier than others, but gravity and size tend to all be the same.
One thing that really helped getting into the game was the thought put into the galaxy. Everything that seems unreal in the game is explained in a way that is easily understood. For example, ammo is unlimited, not just because it makes the game more fun, but because technology has allowed guns that don't use traditional rounds. Bioware makes sure to explain not only this, but every other detail. Everywhere you turn, there is more information to put into your "Codex" (like a handheld encyclopedia). This information often explain why species act a certain way or why guns behave the way they do. Pretty much anything you're curious about is explained.
The leveling system seems flawed as well. None of the abilities are all that thrilling to use, and I found myself end up not using biotic abilities that often just because it was easier to pull out my shotgun and blow them away. Core statistics cannot be changed (like speed, strength, dexterity etc.) but instead there are abilities that increase damage as well as other statistics. There are also not too many abilities to choose from, which detracts from the overall feel. One thing I expected was good/evil based abilities, but this was nowhere to be found unless you include charm (good) and intimidate (evil), which only gives minor store discounts and some more dialogue.
There isn't much diversity in weaponry or upgrades. There are pistols, shotguns, assault rifles, and snipers. The only character that can use all of these to their full extent is the soldier. All the characters can technically use all the guns, but if a certain character is not trained in using shotguns for example, it pretty much becomes useless because of the heavy accuracy penalties. Another issue I had with the items is that you would literally find five of the same item multiple times in any given assignment. That means you could find the same armor upgrade five times, the same ammo upgrade five times and so on, all within the same mission. This makes opening crates and such pointless, and makes earning money from selling far too easy.
Overall, Mass Effect is an immersive game that doesn't quite deliver what you would hope for. Mind you, it's still fun to play, but it's not quite what you'd hope for. It's undoubtedly better than the sum of its parts, simply because the parts aren't all that great. It's worth playing, but not really worth the wait.