I have played Trains several times, and I enjoy it. It's unlike Dominion in that the game is more about timing than assembling particular combos of cards. As other posters have noted, the VP cards give fewer points, and give extra waste, compared to Dominion. The cheap points are to be found on the board--but to take advantage of those, you need to play actions to take advantage of them. You start out with a few of those cards, and you can buy more, but they do give waste when you play them.
So should you wait to play them? Well, you'd like to wait until your deck is well-developed, but you also need to weigh the fact that if you want to build into a location after someone else does, you have extra cost and get extra waste. Some games, you'll wait and other games you'll hurry.
(A lot of reviews make a big deal about the ability you have to spend your entire turn to dump the Waste in your hand. My sense is that this is not typically going to be an important part of the game unless you are playing a slog-type strategy and are fortunate enough to get your Waste to clump up relatively early on.)
For the most part, I appreciate the removal of Actions and Buys as separate concepts. It moves the focus to the board and introduces some interesting design space--there's 2-cost cards that wouldn't be viable in Dominion but are cool in Trains (there's a Treasure-analogue that is worth $1 but $2 if you have a Copper-analogue in play.) The Lab-analogue and double-Lab-analogue (cost 7, draw 3) are powerful and important if there are cards on the board that have good synergy (i.e. usually) and the Tourist Train (Copper that gives 1 VP when you play it) is always a big deal.
If you're a Dominion expert, you'll also be good at Trains, and possibly the biggest reason is that you'll understand the importance of controlling the end of the game. Often there are cheap piles that are in demand and the lack of Buys as a necessity means that you'll often have a lot of control over the end of the game, especially if you're playing an "engine"-type deck as opposed to a "slog" that fills itself up with Waste.
Maybe the biggest reason I enjoy Trains is that I've played enough Dominion that playing with novices is unsatisfying for everyone. They feel outclassed and confused, and I feel bored and unchallenged. Trains is familiar and doesn't break Dominion just for the chance to break it (i.e. there's no second currency called "fighting" or some such crap), but is unfamiliar enough that it's an interesting experience for everyone. Will I end up playing it 1500 times? Well, probably not, but I have little doubt that I'll get my $40 worth out of it.