I was unsure about purchasing this game initially, but I'm glad I did. Although the gameplay looks quite simplistic, it turns out that there are many different tactical possibilities. Each level can be a bit of a puzzle to solve, and the solution often comes down to building a different deck. If at first you don't succeed, change the cards in your deck. Even so, you could have a good deck but still lose due the random chance of which cards are drawn. The first few cards are often crucial at the start of a battle, but don't give up, I've come back from some bad starts and still won.
Card games are usually turn based so I was a little surprised to find out that there's a fairly quick timer running constantly (with no pause unless you press escape, but you can't study the board while paused), so you have real time pressure forcing you to make quick decisions. Normally I hate this sort of thing, but in this case I actually like it. It didn't take long to get used to it, it ensures quick battles (which makes a nice change of pace for me because I normally play slowly) and while it puts you under pressure, the timer lasts long enough for you to make good decisions most of the time, although occasionally you'll mess up.
My advice is to have a clear strategy in mind before you start each battle (and construct a deck to support that strategy), so that you know exactly what you plan to do during the battle. This makes it much easier to make quick decisions. Often you'll lose each battle on the first attempt, usually because the deck you're using isn't appropriate for the new situation, but just treat that as a learning battle to help figure out the best strategy to win it.
Each battle often has 3 different victory conditions. You only need to win the battle to progress the storyline, but if you fulfill the extra victory conditions you win more cards. Often you'll need to play each battle 2 or 3 times to win them all, since you usually need to win some new cards to help you fulfil the extra victory conditions.
There's a multi-player option and some cards can only be won by using this option. I'm not normally a fan of multi-player but this game seems ideal for it because of the fast play timer and the short games. I also think that playing against another human with a custom deck would make the strategy a lot more unpredictable and hence interesting.
I've only played through about 10 battles so far so I'm not sure how much more the game has to offer yet. I may add to this review once I've played more.
My conclusion so far is that the gameplay and tactics are better and more varied than I expected and it's proving to be quite an addictive game. I recommend it to anyone who enjoys the random nature of tactical card based games, and the ability to create custom decks and play multi-player.
[Edit] I've finished the main campaign now, there's 19 battles in all. Later battles become extremely difficult and can be frustrating to complete. But they're all winnable, the key comes down to designing an appropriate deck, but even then it may take several attempts due to the random nature of card drawing. In spite of the difficulty, or rather because of it, I found winning to be even more satisfying.
I still haven't beaten all the battles with the extra victory conditions yet, but I'll be going back to do that. Not only that, but once you've beaten the campaign once, you can play the entire campaign again at a higher level of difficulty. I've spent 21 hours on it so far so there's plenty of value to be had from this game, and that's not even mentioning the DLCs which add new campaigns.
In response to some people who've said that there's not much depth to the strategy, they're wrong IMO. There's a massive number of different ways that you can construct decks and many different strategies you can use, you just need to use your imagination. For example, the rubbish prototype ironclads you get at the start of the campaign often came in very useful in the difficult later battles, simply because they are so cheap (you can spam them and use them as blockers).
So my final conclusion is that I highly recommend this game, provided you enjoy the random nature of card games and can handle the stress of the fast turns (you have about 3 seconds in which to play cards each turn, plus another 2 or 3 seconds to resolve the turn).