There's a few things about The Mirage, but overall I really enjoyed my stay here.
I was here for 2 nights, a Sunday and Monday, with my mom and sister. We requested a non-smoking room but had concerns about the smell anyway, since smoking is still allowed in the casino. For $20/night, we were able to upgrade to an "executive" room that wasn't a whole lot bigger than a standard, but definitely worth it. It was clean and smelled just fine (good in fact) and had a really nice bathroom with a walk in shower and jacuzzi bath tub.
The casino is a little meh. It seems oddly outdated and it's very, very smoky. Just walking through it, the smell of cigarette smoke is a little overpowering.
Overall, The Mirage is a nice choice for a stay in Vegas, particularly for it's central location on the strip. Make sure to see Beatles Love while you're here!