Excalibur is a nexus for two of the worst types of Vegas tourists - lushes who want to go as cheap as possible on their Vegas Strip Va-cay, and people who think it's a good idea to drag their screamy undisciplined kids on a trip to Vegas. And it has a mild but grunchy smell all throughout the gaming floor, beyond the usual cigs-and-coconut "eau du casino" ... there's like an odd fried food edge to it or something.
That's about it, though. If you can deal with all that it's OK enough for a 3, at least if you can somehow get a decent price (and you'll have the best chance here of all the MGM properties short of Circus Circus, as this is considered their second-lowest-tier only to that one).
I spent one night in the Resort Tower (the most basic one), on one of those "comped but you still have to pay the $32 resort fee" offers. Was on a weekend though so it was a pretty good deal. Check-in line was surprisingly short too, at least if you get there just before/around check-in time. Later on it's probably awful, I know it was over at the Luxor around 5 PM the one time I stayed there on some random weekday.
The room is at least a small step up from a budget motel. Better bed, and the wifi is surprisingly fast and good for a system that is open to anyone in the casino (not just hotel guests). Bonus points for the bathroom ventilation fan, which you rarely see in casino towers for some reason. Basic otherwise. No coffee maker or fridge.
Gaming floor is whatever. Food is all expensive but that's the entire Strip. At least the food court has plenty of seating and you can just go kick it there for an extended period if you want to sit down.