You know, me and one of my friends were having a big discussion about Mass Effect the other day; we both really enjoyed the games, but both agree both games were a little 'off'.
Mass Effect 1's combat could be a bit clunky, but it worked, the RPG elements were fairly strong, the story was great. To make it a better game needed slightly more appealing combat and more unique items rather than ItemI-X
Arguably Mass Effect 2 streamlined too much, the RPG elements were heavily toned down, and the game felt much more like a reasonable shooter with some RPG elements, not to mention adding clips back in after infinite ammo in the first game sort of made sense from a gameplay point of view, but felt really wrong from a progression/universe point of view.
Story was arguably more epic on the first game, while a little more 'closed in' on the second, perhaps suiting the playstyle, and I'll admit to being a bit 'well...I kinda saw that coming' and a bit dissapointed with one 'revelation' in ME2. Both are really good games, I just hope ME3 is a better blend of what made both games great.
Strong Story and RPG elements from the first, with faster-paced action based off the second, with some improvements to the pacing and how repetive it could feel at points (as mentioned above it could often become a bit predictable).
Hopefully we won't be let down, and Bioware will learn, I think from the feedback they'll probably realise that perhaps they still need to get the balance more on the spot, they do seem to care about this franchise.
Being able to romance Tali in the second game was OBVIOUS fan service as well, because most people I know who played the first game found her more likeable than either Ash or Liara...not that I'm complaining; she was probably the most likeable of the females in both games haha. Ironic given you never actually see her. Bioware really teased people with that one too, I kinda hope they reveal at least what her species looks like come the next game.
I'd say go for ME2 over FO3:NV, as by and large I'd say ME2 is PROBABLY the better game, not that it's perfect. It probably is one of the best games out this year too, I had to wait til recently to play it, and I definately enjoyed it despite not playing it during the rush earlier in the year.