Haven't had any lag problems. I'm definitely getting some graphical issues here and there (like that little scanline thing, assuming that's the right name for it). And the whole thing is feeling a little drab. It's also feeling really fetch-questy at the Citadel in the earlygoing. But the writing and voice acting is really strong and the way the story's unfolding makes it clear I'm in good hands, storytelling wise.
Combat feels kinda rote--so far I'm just lining up shots and mashing the button a bunch. Not sure I love the sticky cover system--I think those tend to work better with a dedicated key.
I'll definitely keep playing. I'm not lost in it like I can get with some games, where hours melt off the clock in the blink of an eye. It feels a bit more laborious than all that. But it's early!
First thing I'd do is turn off film grain in the options. It's a pretty poor effect (and a lot better in the other two ME games) and also motion blur, which I turn off in every game I find it in. Motion blur should be left for consoles or integrated graphics cards.
Otherwise, yeah. The Citadel can seem like a bit of a drag, especially early on - You're dumped into a Galaxy's central hub without any real idea of how it operates so you can be darned sure that Bioware will give you a crash course in galactic race relations. Do as many of the side quests as you can manage - the flavour that they add is just that, flavour.
Combat's not great and easily the game's weakest point. I've not seen a mod to fix it either.
Thing is though, I'll put up with ME1's pedantic nature and numb combat every day of the week because, at its core, it's a proper Bioware RPG. ME2 and 3 are slicker, better looking and handling games but they're dumbed down to the point of being Bioshock with dialogue trees. Fine if that's the experience you're after but the lack of inventory control and dumbed down levelling options are, for me, a huge debit after the credit built up on the more superficial aspects.
They're good games (I think ME2 is an excellent game for what it is) but they're barely RPGs at this point. Were Bioware intentionally hamstrung by their new paymasters?
The rafts of awful DLC (apart from Lair of the Shadow Broker - that thing is one of the best bits of DLC I've ever played) suggest that this was the case.