The X-Wing expansion is a nice addition to a fun game. As noted in my other reviews from this line, you can play a few simple and worthwhile games with the core set, but if you want to get the most variety out of the game you'll need some expansions. Because the X-Wing also comes in the core set (which is required to play), it is not 100% necessary to get this expansion set to get the most out of the game. But, there are a few additions, so I'd say it is probably worth getting one of this expansion set for most people (if then, if you want more X-Wings or TIE Fighters I'd just buy extra starter sets to get more bang for your buck).
That said, the X-Wing expansion adds two unique pilots that are NOT included in the core set. Pilots include Wedge Antillies (unique) and Garven Dreis (unique). It also includes two generic pilots that come with the core set.
Wedge alone makes this expansion worth getting in my opinion, as he is the highest ranked (Level 9) Rebel pilot in the game, with an awesome offensive special ability, "When attacking, reduce the defender's agility value by 1 (to a minimum of `0')."
Garven is a level 6 pilot that also has a very nice special ability, "After spending a focus token, you may place that token on any other friendly ship at Range 1-2 (instead of discarding it)." Based on the FAQ that was recently released by FFG, it is possible for him to give a focus token to a ship that already has a focus token (which definitely adds to his value).
It also includes several upgrade cards (many, but not all, of which are also available in the starter or other expansions). The expansion includes two astromech droids (R5 Astromech, and R5-K6), Expert Handling, and Photon Torpedoes.
The expansion also includes all tokens, dials, etc. that you need to use this ship in a game.
As noted in all of my reviews of FFG X-Wing products, all the ships look great. However, the X-Wing seems particular fragile because of its thin guns. I've played about a dozen games and haven't had any problems with any ship breaking so far. I am not rough with the ships, but I am not overly careful with them either (except perhaps when storing them).