Yeah the combat in ME1 was really clunky, but the game overall was just... magical. The story is one of the best I've ever experienced, the character development was really good, and the atmosphere was breathtaking. I know the Mako side quests were little more than re-skinned copy pasta, but I still find myself staring at the screen and imagining a place in the galaxy that looks exactly like what I'm looking at in game. The main missions had some funky pacing, but they were still emotionally engaging. I found Noveria kind of repetitive, but the battle on the Citadel still makes me hurl insults at the Geth and at Sovereign. Virmire is still gut-wrenching, and Ilos is just amazing (Vigil ftw). Even the Normandy SR-1 was amazing, it actually FELT like a warship! The SR-2 from ME2 felt like a cruise liner with guns, and in ME3 it felt like a repainted cruise liner with guns. The SR-1 is the best Normandy hands down. Years and countless playthroughs later, I still find myself saying "wow" while playing ME1. It's still magical for me.
ME2 was an amazing game, but it felt hollow in comparison to ME1. The game mechanics were greatly improved, but the mystique from the first game was gone. More characters to develop was a definite plus, but the game as a whole just felt different. It was lacking something that I just can't describe. The mission pacing was excellent, but they felt unrefined and had virtually no emotional engagement. There is not a single moment in any ME2 mission that sticks out in my mind, except the DLC missions. Lair of the Shadow Broker was perfect, and Overlord is almost as good. ME2 still has high replayability for me for the game mechanics, but the quality of the story pales in comparison to that of ME1.
ME3 for the most part managed to recapture some of the magic from ME1, but not much of it. It felt richer than ME2, but the story felt rushed and somewhat empty at times. The Rannoch and Tuchanka missions were pure brilliance and just downright fun from beginning to end, even more so than Lair of the Shadow Broker.
(Wreav: "Kalros must be smelling fresh Salarian meat." Mordin: "...or Krogan halitosis!") If the whole game was like Rannoch and Tuchanka, it would be a masterpiece. That said, there are some missions that are pretty shallow. The panoramics of Thessia recapture the awe of some of the Mako missions from ME1, which is why it's one of my favorites, but it is still a pretty shallow mission unless Javik is there. The mission with Aralakh company has some amazing gameplay and one of the more emotional moments with Grunt, but the Rachni Queen is glazed over regardless of your decision in ME1. The Citadel is bigger, but feels emptier. The Sanctuary mission is quite good, but the whole Miranda/Henry Lawson thing feels like a footnote when it should have been a chapter of its own. The final mission on Earth has kickass gameplay, but the story is severely lacking. This mission SHOULD have been the crescendo of the game before the resolution, but it is severely lacking the necessary emotional engagement (I know I say this a lot). For comparison, the Suicide Mission (ME2) and Ilos/Battle through the Citadel (ME1) was one HELLUVA crescendo for the ultimate resolution to each game. A lot of the goodbyes feel half-hearted and ingenuine. Only the goodbyes from romanced Tali or Garrus (either bro or LI) are really memorable (I romanced Ash for the record). Jack, Miranda, and Grunt deserved more than a vid-comm goodbye. As for replayability, I expected to be a slave to ME3 for months going through all of my different Shep builds, but after one playthrough I'm done. It is just too depressing for me to see this whole journey have such a hollow, empty, and meaningless ending. I originally liked the ending a lot, until I thought about starting a second playthrough and realized how worthless the ending really is.
To sum this whole thing up -
Story: ME1 >>>> ME3 > ME2
Gameplay: ME3 > ME2 >>>> ME1
Wow Factor (aka "magic"): ME1 >>>>>>>>>>>>>>>>>>>> ME3 > ME2
Characters: ME2 > ME1 > ME3
Character development: ME1 > ME2 > ME3
Mission pacing: ME2 > ME3 > ME1
Emotional Engagement: ME1 > ME3 >ME2
Normandy: SR-1 > SR-2(ME3) > SR-2 (ME3)
Replayability: ME2 > ME1 >>>>> ME3 (this should concern Bioware/EA the most)