I always viewed it as an action/fps game with some RPG elements. At least 2 and 3 for sure.
It is more of an action RPG, definitely not a true RPG. That's probably another area they screwed up. If they had spent as much time on the story for the sequels as they did improving the damn gameplay and adding MP then we would have gotten much better games.
You could play ME1, skip ME2 and not really miss much.
Only because of the direction they took the 3rd game, which is another one of its many, many problems. ME2 was a great game with good characters and would have led into a great end to the trilogy if the writers didn't develop an extra chromosome before writing the third game. But ME2 did have its problems as well. I'm one of the few who think that the first game was the best of the trilogy, not the second. The first game had a purity to it, great characters, great plot, great everything. The sequels only beat it in gameplay.