In its purest form the Pokemon Trading Card Game is just that: a game.
When played competitively, however, the story is much different. I played the game for four years of my life and I tell you it's incredibly luck-based. That's not to say there isn't any skill involved, but there are many facets to the game where skill isn't involved. The game is probably 60 percent of skill, about forty percent of luck. I've lost to enough noobs to know that this is true. The player who has been playing for much longer and understands the game on a deeper level does not always beat the player who's been playing for about a year and understands how to play the game decently.
What have you with coin flips, having to draw everything you need at the right time, bad hands, etc. the game is incredibly luckbased.
Is it gambling? No. In gambling, which is a fair system providing you're not playing at some rigged casino, you pay money, and if you strike it lucky, you are payed a handsome amount of money for risking it in the first place. With gambling, more times than not you'll fail, but sometimes you may get lucky. For example, an example of fair gambling is betting 5$ (or more, or less) against someone else's 5$ and then calling a coin toss. If you call it right, you get your friend's 5$. If you're wrong, you lose your 5$.
The Pokemon TCG requires you to spend a lot of money if you want to play the BDIF (Luxchomp). A few other decks are cheaper, but the majority of metagame cards will cost you a little bit. The unfair part is that, if you win, all you get is a scholarship. You don't make any money by winning it, although your education is payed for. This is only if you do well at nationals and worlds, though. There are no cash prizes, and thus the game isn't fair.
In my opinion, the Pokemon Trading Card Game is actually worse than gambling.