Ok, so I've just finished my first playthrough of Mass Effect 2, and with it fresh in my mind, I started a new game on Mass Effect. Heres what I think....

Graphicly, ME2 is far superior, and the enviroments feel more "alive". I did miss the exploration side of things, and the absence of the Mako was abit dissapointing aswell. Bioware did give us the Hammerhead though, but I miss being able to exit the vehicle and mine resources. Somehow, holding down the Y button over a yellow circle, just isn't the same! The thermal clip idea, imo is offencive, I mean, in the first game, you could shoot your gun till it over heated. In the second ME, I found I was running out of clips 3 minutes into a firefight! Just hoping Bioware scrap the thermal clips! LOL!!
Also, I miss the flow of ME1, the elevator rides, the mission de-briefs with your squad (The second Normandy has a briefing room... so I don't see the problem!) Using the airlock, (again, The Normandy SR2 has this too, yet its purely decorative!) I also didn't like how at the end of missions, I had to read the summary, whilst staring at the back of the Illusive Mans head! Hope they scrap that too!!

Re: exploration... I hope Bioware scrap the "probing" mini-game...that was annoyin as hell... flying the little Normandy around star systems, felt like I was playing Asteroids... without the shooting part! I bet most fans want to return to being able to fully explore planets again, and not just see "parts" of planets. Bioware where very clever in introducing the shuttle into the game...that way players had to go straight to the mission objectives I loved driving about, collecting resources and fighting Threser Maws! I know theres a Therser in ME2, but somehow, hiding behind a pillar, waiting for the T.M to pop up either side of you just didn't feel the same! I just hope ME3 is a nice blend of the first two games, then IMO Bioware will have an epic game, that people can play over and over again!

Thats my two cents anyway!