Well, I got 6 hours or so racked-up onto Hitman: Absolution just last night alone.
I have NOT touched Contracts mode, but I'll speak a bit on the Story Mode (Campaign), from my first impressions of those hours.
If you've played previous Hitman games (namely say Hitman 2: Silent Assassin; Hitman: Contracts; Blood Money - since I've actually played all of those), Absolution is definitely a DIFFERENT kind of Hitman game. Some things are similar; while some things are just NOT.
Mission objectives...might differ. They are NOT always "Go kill specific enemies" like most missions in the older Hitman games. This ones tries to mix it up a bit more. Some missions are basically "Get the hell out of the area", "Evade the cops" or "get to the next floor." So, sometimes, this game comes off w/ levels being smaller in size and even more linear - b/c there's a bunch of these kinds of levels.
Sometimes, then it's the opposite - feels like something out of the older Hitman games. You'll get these big sand-boxy open-levels (I'm thinking like say the Chinatown King level) where you've got tons of ways to actually finishing off your mission's kill(s) and/or exiting the level.
{If I recall, when the game's actually teaching you to play - they mentioned you could finish the Chinatown King at least 12 different ways!}
I expect in levels especially like these - replay value is definitely through the roof. If you look at Challenges list (F1 key) while in a level, you're going to see TONS & TONS of Challenges. Oh, and the game has 47 (ha!) Achievements listed.
Things worth noting - there's a cover system in here. 47 can vault over cover; shoot/attack while in cover; move from cover-to-cover; and all of that kind of stuff. Seems appropriate to have, since he's an assassin and trying to hide in the shadows and kill silently and all of that. If you walk-up to an enemy and want to engage in hand-to-hand combat w/ enemies - these are now QTE's, more or less (i.e. think like Witcher 2's boxing/fist-fights).
Also, for most missions - you're CONSTANTLY being rewarded points & docked points, based on your actions. If you're playing this game online, you are being compared to the game's USA Leaderboards and World leaderboards; and your Steam Friends list. If you actually do care about your score - you'll probably either be reloading saves A LOT or going to wind-up REPLAYING levels. My first time around w/ this - so, I'm not caring too much. I'm playing on Normal and trying to go through the game level-after-level. I'm...honestly, not playing well compared to the rest of the USA/World/My Steam Friends, hehe. You obviously want to NOT be spotted (that knocks MAJOR points off); clean-up any knock-outs/kill you make (i.e. throw them in a garbage bin, push them off a cliff into a water, throw someone in a mud bath tub, etc) so you can actually get some of your points back; and try NOT to kill civilians (you get docked MAJOR points for killing civilians). I should note - the harder DIFFICULTY you play on, the more BONUS points you get for completing objectives. Once you a finish a chapter, you unlock it - so that if you want, you can select a chapter and then go right into that mission.
There's an Instinct meter - that fills up while you play. Depending on what difficulty you're playing, it might be there (Most Difficulties - but how it can be used and if it recharged might be differently tweaked)...or it just might not be there as an Option at all (i.e. Purist). Instinct lets you do all kinds of stuff. You can see enemies' through walls - a la Batman: Arkham Asylum & City. Also, Instinct can show you pathways of NPC's, as well - again, that depends on Difficulty level, as well. Instinct can also let you do Tag & Execute kills like Sam Fisher could do in Splinter Cell: Conviction, as well.
The game has checkpoints scattered very sparingly throughout levels. Also, depending on difficulty - you might not even have any save checkpoints even allowed (i.e. Purist).
You don't really select your weapons at load-out, either - unlike most Hitman games. You'll find A LOT of different items/weapons/things to use in the game-world, BTW. In Hitman: Blood Money - you earned $$ for each level and could then spend it on buying and upgrading new weapons; in Absolution's STORY Mode, this is just NOT here.
Also, the story in this Absolution seems WAY more focused in some things, compared to other Hitman games. While I ain't played it all the way through, this game seems to have less globe-trotting and now be sticking in the USA more so than ever. So far, I've only been in the USA - though, the areas themselves have been diverse (Estate, Chinatown, Hotel, etc). Also, this game seems WAY more story-focused and story-driven than previous games - and actually have a bunch of reoccurring characters within this one story.
So, there's my thoughts, so far on this one.