Things Mass Effect should have done better...

Audio - While the voice acting and music are top notch, the other diegetic audio in Mass Effect is merely adequate. The weapons sound effects do the job but they aren't memorable. Many of the creatures make the same cries over and over again. Also, dialogue outside of the cinematic conversations is often too quiet, overshadowed by the music. Most problematic is the lack of ambiance, though. The world seems very quiet, which does not strike me as realistic for an environment teeming with life.
Downloadable Content - Fans were probably hoping for more downloadable content from Mass Effect. We got one item so far, and to its credit, it's pretty well done, however one DLC mission in over a year is not very impressive. Apparently they're planning to release one more package to tie Mass Effect 1 and 2 together though it will focus mostly on combat, which is another part of the game that needs work. Combat - The shooting gets repetitive pretty quickly. It brings nothing new to standard shooters though it does not control as well as most of them. The enemies all walk forward in the same stiff stances and are not inflicted with wounds when they are shot, making the weapons seem ineffective. It would be nice if I could blow chunks out of a geth's torso or blow a batarian's head off. The game is rated Mature, so they may as well make the most of it. NPCs - These are one of the many well-done things in Mass Effect, however, improvements could be made. More animations would make their actions more unique and realistic. Also, their eyes often appear to be staring in multiple directions, even though they look real and have character. Exploration and Environments - I'm tired of riding the elevator. The dialogue is good but I'd rather see it in an interactive conversation than while standing stiffly in a slowly moving elevator. Off of the Citadel, there are not even conversations or news reports to keep you interested while you slowly make your way between floors. It may be a necessary evil to disguise loading times but if the designers are creative, I bet they can think of a few other ways to mix things up a bit. Next, driving the Mako around uncharted worlds is just a pain in the ass. Often times it will move forward without you telling it to and end up off a cliff or in lava. It's a tedious way of getting to your objective. What's worse is the terrain you traverse. It's all so similar and all so mountainous. It's like they just made a bit of random relief and just pasted a different texture on it for each world and added a different weather effect. Personally, it makes the game less immersive by making me well aware that I am playing a video game and not walking on the surface of the moon. Side Quests - The biggest problem for me in Mass Effect are the side quests. They don't serve much purpose other than helping Shepard gain experience, level up, and do some more shooting. Very few of them have interesting plots to them and they don't really help develop any of the characters like those in KotOR did. They also seem to be less important than stopping Saren and Sovereign from destroying the galaxy. After all, would Commander Shepard really bother to hunt down a murderous geneticist when the fate of trillions hangs in the balance? Perhaps if the main plot wasn't so imminent, he would be justified in doing so or better yet, if the side quests were more tied in with the main plot or if the player would gain something by doing this besides boring equipment, they wouldn't be so bad. Ultimately, they just don't feel relevant to the core story.