Hm. Predicament we are in. I've put in over 500 hours in both games. (for creds)--added together lol
PROS-
DMC3:
Better Story
More Combos/Manual Combat System
Instant Weapon Switching and Canceling
More boss fights
Better sense of Balance (I'm looking at you Flying Swallow)
Heavy RPG/Character Building Elements
Castlevania 'vibe'
Allows you to Carry over stats for added replay value. Boss Tactics and enemies change on harder difficulties giving the game more depth.
Kick ass cutscenes
Ninja Gaiden:
Friendly Save System
Better Graphics
Difficulty that isn't insane for your average gamer
480p
widescreen
More Varied level design
Fun 'adventure' segments, no crap genre breakers like in God of War
Moderate RPG Building Elements
Amazing sense of control and defense in the action.
Amazing Wall-Play Combat.
CONS-
DMC3:
Checkpoints cost money
Difficulty is extremely high front to end even on easy mode, thus killing the fun factor for non-DMC fans/novice gamers.
Ninja Gaiden:
Lame Automatic "Dial a Combo" system. However it has amazing defense oriented combat. XYXY XYXYXYXYX XYXYXYX based combos blow chunks.
Lot of backtracking
Some uninteresting level designs (a bland looking town etc.)
Some "WTF" platform moments.
Balance issues, some moves are godly that can be massively abused on normal.
LACK OF CARRY OVER STATS (a big no no for me)
Shit ran over twice as a story
Boring lead character (does the dude ever talk)
That's all pointless really, looking at general appeal and influence both games are quite excellent and I'm sure you knew that before you made the thread. I will say however, get DMC3. Yeah, DMC3 is 'perfect' for hardcore gamers, but more importantly Ninja Gaiden Black is coming out. For you to buy Ninja Gaiden for 30 bucks, and then have a superior version (at 30 bucks mind you) come out a month or so later --is one big suckage-- for you.

Get DMC3 now. Sell a pint or two of blood a few times, and get Ninja Gaiden Black when it comes out a few months from now, or is it next month?.
Close thread. The C- Warrior has spoken on the essence of action gaming. If people keep posting in this thread, I will write a thesis on the pure essence of action gaming.
PS:
www.thehandvseye.com
Great website to get the flora and fauna, to see HOW DEEP and intense DMC3's combat mechanics can truly get. It's a sight to behold.