My parents and I are going to Cancun for the first time this coming February. We will have a car and be staying at the Westin Langunamour. We will be there for a week and have some idea on what we would like to do. We would like to see Chichen Itza, Tulum, Ik Kil, Playa Del Carmen, Isla Mojores and maybe Xcaret. Is Xcaret worth a day visit? Also, how is the weather typically in Cancun this time of year? Can someone recommended some great places to snorkel. Also, what shouldn't we miss? Also, do whales come down this way? Thanks!!
It seems like your week is pretty busy already. Chichen Itza is not terribly close so it will take you at least until the afternoon (assuming you leave at the crack of dawn) to get back to Cancun. I would recommend stopping at Vallodolid on the way - it's a lovely historical colonial town (totally different than Cancun which was made from scratch in the 70s). Check out the Casa de Los Venados when there, it's a really unique private home with tons of Mexican folk art (need to reserve first - http://www.casadelosvenados.com/#)
Also there are (swimming) sinkholes called cenotes along the way as well. Great idea to see the Tulum ruins - stop by the town itself too, it's worth it (you'll several cave diving and snorkeling outfitters there). It makes sense to pair it with Playa de Carmen because it's on the way. You'll need to take a ferry to Isla Mujeres so your car will be dead weight that day. You can easily spend the whole day in Isla and tour around in a rented golf cart. I did all those trips (minus the island) by bus via downtown Cancun - it was easy and the buses were really nice.
I haven't been to Xcaret, so cannot comment (except that it looks like fun, big water park - lots of kids and families). You should leave at least a day to bum around Cancun itself and hit the beach. Cozumel seems like a natural place for snorkeling; there are likely others.
Yes, it will be hot and humid so be prepared (hats, cool clothing, water). And bring insect spray. And when you're driving, watch out for huge speedbumps on the road called topes. They are everywhere and quite effective too.
Chichen Itza is well worth a visit and you need to plan at least 2 or 2 1/2 hours on site to really see it all. As Agnes commented, it is not close by. Plan on about 4 hours driving each way. You really need to set out as early as possible in the a.m. to miss as much of the crowds as you can. It is a great place to visit and well worth the long drive. Just plan on a looonggg day.
There is a Chichen Itza, Valladolid, and Ik Kil day tour package I went for which was pretty good. It includes transport to and fro Cancun and entrance fees, costing approximately 45 USD or 60 USD (can't remember exactly).
Apart from that, definitely visit the places along Riviera Maya (from Playa del Carmen to Tulum). There are many great places to snorkel. Akumal for the sea turtles, Cozumel has one of the clearest blue waters (but when I went, it was choppy), and you can snorkel in the cenotes as well. I did in Dos Ojos Cenote and it was amazing.
I also visited Casa Cenote but Dos Ojos is definitely more impressive. I did not try Xcaret though, but I'm sure they have plenty of tour packages to choose from.
Tulum is just a short collectivo ride from Playa del Carmen (30-40 MXN per one-way ride). In Tulum the beaches are less crowded than Playa del Carmen, but there are some good beach clubs in Playa (I spent many afternoons at Lido Beach Club). Try the mango fish tacos!! They are delicious.