Competition is tough if you're looking to open a sushi joint in Vegas, not to mention an AYCE one. I've been to great places and to pretty unsatisfying ones; Umiya sits somewhere in the awkward middle, dangling towards the unsatisfying.
I'll be brief because this place was not very memorable.
The Good:
Decor (Very nicely decorated, lots of space and table room)
Salmon nigiri
Ika Nigiri
Yelp check-in = free drink
The Bad:
Service (No one even looked me in the eye, let alone acted friendly, aside from the lone waitress)
Yellowtail (Not horrible, but probably one of the worst I've had in Vegas)
Ikura (Noticeably small and tasted kind of funky)
Charge for hot tea
The Okay:
Everything else we ate (all nigiri, mochi ice cream)
Presentation (ex: tuna poke was haphazardly piled onto the place with seaweed salad, looked unappealing, bad cuts of fish)
Fresh oysters offered only for dinner even though it's not indicated on the menu like other dinner-only items. All specials only for dinner as well.