Pros: No add-ons required.
Cons: Nothing really.
First thing first - if you plan on buying this, make sure you have the time to assemble it before showing it to your child. I did it by myself one night and it took almost 2.5 hours. You have to assemble the table, drawers, and every building too, and then lay out the track according to the diagram. It's very well labelled though, and I was never stumped at what to do next. You will also need a screwdriver & to recycle a bunch of cardboard when you're done.
Second, you're probably wondering just how big this thing is -- you'll want enough room so your child can walk around it, and open at least one of the drawers (located on the long sides). It is about 17" tall and 33x50
As I mentioned, it does come with 2 drawers which are nice and big - I have a few extra trees and people stored in it, and the track layout, but not much else. We leave it all assembled all the time.
I can't count how many pieces it comes with, there's so darn many, and it's so overwhelming opening all the boxes. The main attractions are:
A mountain with tunnel, sound effects and waterfall painted on.
A hill that slides down through a building with a swinging door & sound effects, and helicopter landing on top
A gas station with attendant that moves in and out
Bridge with sound effects & lights
Crane that lifts items with magnet
The round house
a switch track
It comes with a good assortment of trains, cargo for in the freight cars, trees, people, helicopter. You don't NEED anything more than what it comes with, but you may choose to purchase some 'Thomas' items to go with it. It's compatible with Thomas wooden railway (which I think also means it's compatible with brio & ikea)
Some of the sound effects operate on button cell batteries included, and others require AAA batteries.
The kids had some take along thomas stuff, and it didn't provide nearly the same play value as this does. They love the hills, tunnels, bridges. My girl plays with it more than my son even, and she has her little animals riding in the train cars. They are 3.5 and 2.5 years old. We've had it for about 2 months now, and they play with it as much today as the first day they got it.
It often comes on sale at toys r us - In Canada I think it's usually $199 and is often on sale for $149, and I've seen cheaper at christmas ($129 I think!), so don't pay full price.
The instructions only provide for one track layout, and the design on the playing surface is laid out to match with that layout. I don't think that bothers me though.
I had originally planned on glueing it all together, but the kids don't take it apart, and it hardly comes apart on them. Some kids that visit though only have the intention of ripping it all apart, so depends on your child I guess.
What I love most is that everything you need is in the box, and for the price of just the THomas roundhouse, you can buy the whole thing that is compatible with any thomas wooden railway characters you may have already.