This makes Solforge a unique TCG experience that in some respects eliminates traditional TCG issues, and in other respects exacerbates them. I love the fact that I never have to worry about whether I've drawn the right mana/land/whatever to play my cards. Unfortunately, the same no-cost mechanic means the guy who has all the high-power super-rare cards can drop them all on your head immediately. The level-up mechanic on the cards allows for some really unique card designs, which are fun to work into your deck builds and strategy. However, that same mechanic means that you're even more at the mercy of the shuffler than is usual in a TCG; the player who draws more of those higher-level cards after each four-turn reshuffle has a huge advantage.
Another gameplay feature that sets Solforge apart is its use of a lane mechanism as the playing field. Each player has five lanes, each of which can hold one creature, and creatures attack the opponent's corresponding lane. If that lane is empty, the opponent takes the creature's damage. This lane approach isn't unique to Solforge, but not a lot of TCGs use it. It adds a layer of strategy that other games lack.
Like most collectible/tradeable card games, Solforge cards are obtained primarily through buying randomized card packs. There are four rarity levels: common, rare, heroic, and legendary. The packs handed out for daily for logging in and winning 3 games, or bought using the free-to-play "silver" currency, will give you commons and a rare, and (very) occasionally something more. Using the "gold" currency bought with real money can net you chests/packs with better cards. You can also "forge" cards, turning in your extras for silver or paying silver to create a specific card. The cost is such that you won't be able to afford very many legendary cards this way, but it's nice to have the option. Solforge is very playable as a free-to-play game, and spending money gives you a nice boost; both important aspects of a well-designed business model.
You can play games against a fairly decent AI opponent, or online. I find myself playing against the AI often to get my "win 3 games" reward, primarily because I can actually get through three games fairly quickly that way. If I try to play online, it often takes forever to get through a game, in large part because there's no turn timer. You can play a game where each player has thirty minutes to take their turns, but that's for the whole game. A player might wait twenty minutes before taking even their first turn. I'll try the occasional online game, but if an opponent isn't taking turns every couple of minutes at least, I usually end up conceding and just playing the AI.
Solforge also has online tournaments, which can be entered via event tickets (purchasable or obtained from daily rewards) or in-game currency. The Constructed tournaments are pretty much the same as every online TCG: a few deck archetypes dominate, and unless you have one of those, you're probably going to lose horribly. Without the right cards and a lot of practice with your chosen deck, it's an exercise in frustration - not worth bothering with. The Draft tournaments are more fun for me, where you pick your 30-card deck from random choices and play four games against similarly-equipped opponents. Some cards are still much better than others (you'll get really tired of seeing Darkforged in draft) but at least it's a more level playing field.
I enjoy the unique concepts that Solforge brings to the TCG genre. There's bad with the good, though, which keeps me from playing it more often. Despite that, it's well worth trying out for anyone interested in these sorts of games.