The hotels in the new City Center area of the Strip are everything you want in a hotel: ultra-modern, high-tech, new, clean casino, gorgeous pools and fabulous restaurants. I liked Cosmo a lot. The reason it gets 4 stars instead of 5 is because:
1. I think Cosmo is trying a little too hard to be "edgy" and it comes off as a little contrived.
2. I think Aria has the edge in terms of sophistication and a classier crowd.
Don't get me wrong, Cosmo is terrific but someone who's (ahem) over 30 years old, I prefer Aria. That said, they're both amazing hotels and probably my top 2 choices in Vegas.
The Cosmo buffet is actually better than Aria's, although it pains me to admit it.