That is a good question Toad. Alot of people like BO better and alot like MWR better, it all depends really.
In Black Ops I will admit that the graphics do seem a tad better than in MWR, and the explosions look better and some new things were added that make the game even more enjoyable. And yes with all that you'd think the game would be spectacular? or well at the very least somewhat Original? Well...not really..the maps arn't really 100% different and I highly doubt anyone would even expect the maps to be 100% different. But they are different. Compared it maps I have to say MWR is better. Simple fact is in BO and some people here may not agree with me and stuff and I honestly could care less this is just MY OPINION, but in BO the maps are plain. They are not that great in MWR the maps seem alot more detailed with building structures and such and even places to go the areas just seem wider to me. In BO there isn't that many if at all camp spots for snipers which most ppl probably don't even like campers? but you know what as a sniper you'd need to camp in order to have good clear shots. Now as we all know there is never a 100% clear shot with being a sniper you can take a shot but the only time it is completely clear totally 100% is if the person your targeting is completely still and not moving. (Again just my opinion) thought i'm not a sniper. I primary weapon is and always will be Light Machine Guns. Though I don't use sniper weaponry I DO however snipe with a LMG if I get a good spot. And i'm damn good at it, if i'm focused I can usually even shoot the same as a sniper with the advantage of having a weapon I can continue to pump ppl full of pixel led with lol. <.<...but yeah. Waay off topic I think...
Back on topic..The features are different aswell and yes there is new levels but they also took levels out (As I expected) but again the levels they do have are just to boring for me. There is not really any suspence or curiosity beyond each moment. And even inside of buildings just seems alot more emtpy to me. And ares in BO not only seem empty in buildings but straight paths that have stuff to take cover from fire..well..just doesn't seem like it provides enough cover for what goes on. All in all the games are both different. The decision to get one of them is a good one to make but determining which is the tough part. I say MWR is the better of the two games but BO is still a fantastic COD game. As a COD fan or as DPrinny refered to us COD ppl as "COD Freaks" xDD (Just messin with ya prinny x.x...don't ban me or nuffin plz) I personally think MWR is the way to go. BO is still pretty new so you can always get that, can always get MWR as well but I think MWR is also the better of the two for you to start with. That way when you go into BO you understand alot more of how the levels work and such.
Hope this has helped. But side note. Even with peoples views on the game the choice to buy either is still yours. Our views maybe completely different from how you see either of the games.