Have to admit I haven't played ME3 but I'm familiar enough with the story that I can say I feel ME began with the best game in the series. The second isn't far off though, and of course it looks a lot better. Would have been better too if they'd kept the leveling system and inventory (but with better management - baby got thrown out with the bathwater on that one), kept the Mako but reduced the driving, and never ever thought of the Hammerhead.
Happy to go into it as I've just done my 3rd run of ME2, though maybe not as this is supposed to be spoiler free here. Suffice to say that I'm a story junkie and ME1 and 2 both satisfied in different ways, though 1 a little more than 2 because it did a good job of establishing the universe it's set in 2 let itself down with the ridiculously weak explanation for the reload mechanic - never mind the obvious plot holes, if the important factor in winning gunfights was how many rounds you could send down range as the codex says then why move away from a system where a frictionless materials mod on the right gun lets you hold the trigger down for a whole minute, and if you have the right ammo and don't mind a slightly reduced rate of fire you can hold it down forever without overheating. Just bugs me slightly when you see a series go against its own established fiction. Would have made more sense if the codex just admitted that the ME2 heat sink reloading isn't as good and justified it somehow. They could have retconned things so that the ME1 guns were actually the newer tech and depended on some weird unobtanium stuff, and in the two years Shepard spent dead the unobtanium became in such short supply that everyone was forced to switch to back to disposable heat sinks (would have explained why Ronald Taylor's old crew and Zaeed's antique rifle used them too).