Yeah, it really is super different. In fact, the first game I played from the series was DMC3 and, when I got around to play DMC1, I didn't quite like it. It's got a different tone but more than that, its gameplay felt completely jarring to what I expected. And I think that boils down to what they were trying to achieve with the game, which (like a lot of you have already pointed out) is more in line with Castlevania and Resident Evil than with DMC3 or even Bayonetta (the latter of which I think got way more inspiration from DMC3 than from Kamiya's own DMC).
So yeah, barring the reboot and the half cooked part 2, I would put DMC1 way behind the masterful DMC3, 4 and 5. Not because its a bad game at all, but more because it's game design and combat don't really evoke what 'Devil May Cry' is to me, personally. It's really fun to see the evolution of the series though, it has seen its share of ups and downs and makes me appreciate the existence of DMC5 even more!