Soooo, I finished the game yesterday and can now share a more complete impression. I'll start with the story...
In terms of story/narrative I think the game is more or less OK. To be more precise, the main premise, shown in the two prologue missions (Earth, Mars), is really really bad - badly written and badly presented. After seeing the endings, I can completely understand and agree with most of the rage about them too - they were also very, very bad (for many reasons already stated by others). The short and abrupt epilogue didn't help matters. However, the game is filled with many other well written moments and subplots, mostly related to specific characters (current and former squadmembers). Mordin's sacrifice, Grunt nearly dying, Samara nearly committing suicide, Thane dying, Liara preparing Reaper-related data for future generations, etc - those scenes, I thought, were well written, well directed and emotional. Unfortunately many dialogs and moments related to the main story were badly presented and filled with idiotic one-liners. Shepard seems to shout a lot in this game, which I found sort of out-of-character, compared to his behaviour under fire in the two previous games.
In terms of gameplay, the biggest issue for me is, as I've stated previously, the limited character interaction, especially with the main cast. Hell, I've had more conversations with some minor characters than I had with my past and present crew. The lack of options in those conversations that are there and their degree of automatization are likewise serious issues, but I did get used to them after a while. It's not something I would want to see in any Bioware role-playing game, but I managed to get past them in this one. One other unrelated gameplay design decision that bothered me to no end was the inability to save in certain areas. Most notably during the final mission, where I couldn't even save in certain non-combat areas and was actually forced to Alt-Tab out of the game in order to backup the finale autosave, because of it.
The action is better and I'm glad I can actually stay out of cover for some time during firefights, instead of being forced to always use it or die, like in ME2. The heavy melee is, however, useless in most situations, because it can very easily miss its target. Too bad the heavy weapons were removed from the regular setup and instead given as a one-hit-kill option in some situations where you need to take out one of the more difficult enemies (Atlas, Harvester, Banshee...), otherwise the shooting was fine. I also didn't like that they used the universal cooldown timer for abilities, but the downside can be minimized by managing your weapons' weight.
In terms of visuals the game could definitely use a high res texture pack, or something. As it stands, the visuals vary from location to location, with most of them looking bad due to low res textures and lack of post processing effects, but there were a few great looking ones too. There is a similar issue with the characters in that their faces use nice, sharp textures and generally look good, while their bodies use low-res textures that look bad even from a distance.
The music was pretty good, as was the voice acting and sound effects, not much more to say about this aspect.
Overall, I'd say the game was OK. It's not game of the year material, but it's not boring either. Unfortunately, due to the horrible endings, I don't really have much motivation to play through it with my second ME2 import.