I just finished lol. I love the implementations of my actions in the 1st game (followed light path, wrex lived, Ashley lived) and I only lost ONE! squad mate (Thane T_T thane was epic...) I had Zaeed (download squad mate on xbox live, idk if PC got him) control the 2nd team and Thane go through the vents in the beginning. Used grunt and legion(used them throughout the entire battle) as my squad, Thane died. Had jack make the barrier and garrius be diversion lead and Jacob escort survivors back to ship, No casualties. Almost lost Grunt at the end when the human reaper went down (barley got his hand before he slide off hehe). I saved the station, which im thinking was the wrong thing to do... My game play was around 30 hours. Oh yeah, I had all ship upgrades and everyone loyal except Miranda, because I stuck up for Jack during their fight cutscene. I used my paragon talk option during Legion and Tali's fight to keep them both happy.
Overall it was another epic game by bioware, I can't say it was better than mass effect 1, because without the original, mass effect 2 wouldn't have been the same (I dont mean story wise,etc but the game in general). Also, I have theory... I don't think the collectors are the protheans.. I think the reapers are the protheans, and what the collectors were creating was some false super weapon that was misunderstood. If you look closely at the cutscene right before harbinger (the collector commander) dies, you see a hologram of what appears to be Sovereign, then you hear a voice say "control released" and the hologram disappears. Immediately after you see harbinger shake his head, as if confused, before turning and getting blasted. Also, the cutscene with the mass of reapers... They all look quite similar if all are based off of the creature they were created from, than you would expect there to be a much larger variety of shapes among that mass. I also have the feeling that the Illusive man, may be under the control of a reaper.
Anyways, there is my input and yes.. that is a lot of typing lol
*edit*
Actually... the Name "harbinger" was the one of that reaper hologram, and he had control over the collector commander, you can also notice that collectors eyes stop glowing right after the reaper releases him