Went to see Thomas last weekend and it was AWESOME! I'm sure it varies by location but at least the one we went to in Grapevine (near DFW airport) was really good, and well worth the $18 per ticket (we had to buy 3 tickets, DD was free).
I was bracing myself for it to be rather gimmicky and that there would be an overabundance of overpriced Thomas toys everywhere, and that it would really be a ploy to get you to buy stuff..but that was SO not the case! I think there were some Thomas toys being sold in some areas but honestly I didn't even see them (and neither did DS, hehe). we spent a good 3-4 hrs there and we didn't spend a single cent, not even on food (we just got the professional pictures). It was very much all about trains in general, and just letting kids do all kinds of train-related activities.
There was a little toy train that kids could ride, a huge sandbox with lots of toys, a place where you could get temporary tattoos with Thomas characters, several train & activity tables (some with train setups, others with printouts of characters and crayons, etc). There was even a nice, dark A/C'ed room where they were alternating between showing 10min Thomas videos and someone reading Thomas storybook, and there was a generic train table in there too.
And of course, the train ride itself...DS was mesmerized by it. I wish I could have gotten a picture of his face when he saw Thomas coming down the track (I was holding him, and DH was holding DD). He was begging to get on after that! Once we were on he could do nothing but stare out the window, he was just so fascinated by everything. That day it was very cloudy,and while on the train we passed tons of trees... DS pointed out the window excitedly and said "Look, we're going to Misty Island!" LOL.
Anyway, I would definitely recommend it. I think you can just go there for free and do activities and not pay tickets for the train ride, but for my DS (and DD) the train ride was the best part! He still talks about it, saying "We saw Thomas. We rode on Annie. Next time I want to ride Clarabel."
here are a few pics i took
after boarding the train, ready for the ride to start
nothing particularly scenic outside, but DS *LOVED* the ride, was looking outside the window the whole time
afterwards, i was able to get a good pic of DD with Thomas in the background