We've had this discussion, and I'll forever disagree. Partly because I like being Rambo, partly because I hate micro-managing my squadmates, and partly because the Engineer class exists.
Yeah well it's getting revived because I have nothing better to do at the moment!
Okay granted about Engineer, I look forward to seeing how they manage to make that class worth playing in the sequel.
Similarly I will grant that Soldier is great if you take the Revenant, turn up the Inferno Ammo, and waste people primarily from point blank, but if you're going to do that then you might as well go whole hog and bust out a Vanguard with the Claymore because that class is meant to be used that way. If you use the Soldier as efficiently as possible - with Heightened Adrenaline Rush, lots of sniping and mid-range assault rifling - then the mechanics of the game revert to those of a standard shooter, which is where I think ME2 falls a bit short in comparison to many other games.
The game feels at its best when you're in the opponent's face and absolutely ruining them, the sounds of battle drowned out by the pulsing of Shepard's blood as you're on the edge of death at every moment. Soldier's hard to get that with, because not only is Soldier the most efficient killing class, it's also probably the second-hardest to actually kill. Add in a complete lack of powers and, Hell, it's no wonder.
I will grant that my perspective on the game comes from playing exclusively on Insanity for the past seven or eight run-throughs, Soldier playthrough included, so that might affect my take a tad.
But if you really want to tear ass without managing your squad? Gotta go Vanguard. Set up Squad Cryo Ammo, turn on Inferno Ammo, and start Charging your way to the glory land.