In fact, we were married downstairs at Mandalay Bay, and had our small "reception" in a suite at the Four Seasons. Unfortunately, service is not what is once was. The last time we were there our room was not clean, and even after the head of housekeeping came, my kitties found a dirty old baby bottle under one of the chairs. Some of the people are wonderful, but many of the people have left - the manager who opened this Four Seasons is now at Green Valley Ranch. The most experienced concierges have left for the Bellagio. It's a shame, as we liked going for a week for our anniversary.
That said, you may not have any problems - it is very spotty. My sister stayed there a month after we did, and no problems, except for room service. It all depends on who is working, I guess.
The pool at Mandalay is great, and you have access to that plus the Four Seasons pool. Tubs are soaking tubs for one. They now charge for valet parking, and we tipped $2.00 per bag, and $3 for valet each time. Room service gratuity is added on to your bill (a service charge plus 18% gratuity I think), but we would tip extra.
Overall, my sister and I have stayed at the Four Seasons in Las Vegas, Newport Beach, and Dallas. Las Vegas is the nicest of these - we wouldn't stay in the other ones again until they are renovated. I have heard mixed reviews about the LA/Beverly Hills one as well - small rooms, service so-so. May I ask why you are going (businees/pleasure), and why the Four Seasons? I may be able to make other suggestions if I know what you are looking for...