I am going to give you the good the bad and the ugly of this game and let you make up your own minds about whether you are going to enjoy Poxnora or not. To sum up this game quickly, I would say it's a cross between a collectable trading card game like MtG, a tabletop minatures game like Warhammer Fantasy and turn based tactics games like FF Tactics and Advance Wars.
Where to start?
One thing I am going to stress to anyone considering this game is that at it's heart this is NOT a casual game. Veteran players have learned an encylopedia of knowledge about this game. Cards are divided into 4 types, Champions, Spells, Relics and Equipment. There are hundreds of abilities and conditions that can used in this game, from the basics like block, dodge and stealth to the obscure like planarbound and encouraged. What does this mean? As a new player you are going to be confused while you slowly learn what all the hundreds of different cards do and how they interact. What this also means however is that if you enjoy deep strategy there is simply nothing else like Poxnora. Once you learn the game the sky is the limit as far as how many strategies you can employ.
Is this Pay to Win?
The short answer is yes, but not in an evil gimmicky cash grab way. Like I said above this game is very much like MtG or Warhammer. It is a hobby and a collection you build over time. Almost everything is available to purchase with in game currency but there is a HUGE library of cards to be had. This isn't going to appeal to everybody, but the people who it does appeal to will enjoy this game immensely because it is such a deep tactical game. This is a skill game and a well made deck of low value cards can easily outplay a poorly made mash up of expensive power cards. So it is certainly possible to find success relatively quickly without dropping any money on this game at all. You build your collection over time with free cards you earn from playing and then you can bolster your collection by buying cards with real money as you see fit.
How do I enjoy this game without spending a lot or any money?
I recommend all new players go through the tutorials and the new player guides that were recently added. These will reward you with free training decks and in game currency that you can use to start building your collection. You can use in game currency to purchase packs and boxes or individual cards, so you can get the best cards for free. There is also a PVP format that restricts to pre-made training decks so that you aren't facing opponents with lots of strong rare cards right away. There is trading in this game so anything you earn with in game currency can be traded away to other players for something different you may want.
My final advice would be to get to know the game and seek out help from the community whenever possible. People will be more than willing to help point new players in the right direction if they ask. There are community run pools of extra cards to help new players get started and a lot of resources on the forums and fansites to help you learn the game.
I highly recommend this game for it's deep gameplay and rich tactics.