I've seen 2 reviews of this game. A player's and PC Gamer's.
I am horribly disappointed by those. They are just opinions of someone who played the game for too less to actually.. get into it, for lack of a better expression. This is going to be long, so if you don't have patience, don't read it. I will explain my experience in SK, I won't be strictly on the reviewing the game part.

I'd like to start off by saying that I've played this game for over one month. Though I played it every day. I have a total play time of 10 days and 18 hours now. I don't believe this is a lot, but enough to "review" it and have a general opinion on it. Yes I joined in the steam rush, trough a friend telling me about it.
In my first day here, when I saw the CE system... "whaaaat. are you serious? this is just impossible and unfair if i dont pay"
That would be any new player's reaction. Whatever, I left it apart for the moment. In the next days, I would use up all my mist in dungeons, then go to sell my loot (oh.. the prices then.. how I miss them and wish I had then what I have now)
I got 3* gear like that. Playing every day, making cr with my mist, then waiting to play the next day. Of course, it was frustrating and I wanted to play more, but I had to wait. Besides my weapon I bought everything. But still, I got help from my friends. We would go on Tier 1 runs every day, and save the money up together. And like that, we both got almost all 3*. But we didn't go into random gates. I made friends. By sitting in Haven and talking. I think this is meant to be part of the game. Get friends, they help you, you help them. It's not a game meant to be played alone.
And then, as I said, I made some friends.. and one of them taught me everything I know. About gates, gear, and how to fight. I observed how he played and did the same. Not exactly though. I didn't understand everything. This game.. depends equally or even more on skill than gear. A 5* player can die in Tier 2 without the required skill. And a 2* player could survive, without dying once.
He helped me a lot. This is where I skipped a lot of gameplay. But I believe this won't make the review unfair. He helped me get the CE to 5* gear. But still, I had to get crowns for the recipes and heat up the items myself. If he had not helped me, I would've just kept doing the same, use up my mist, wait another day.
After I got my 5* set, I started doing Tier 2 dungeons. And they were tough. Why? I still didn't know how to play. I never understood how the others did it. But now I do. You need to learn how to play, how not to get hit but hit themselves. And using the right gear for the right monsters. Though this is not always possible, since you need to aquire it.
The CE system.. is probably the most fair I've seen in a F2P. Yes I got my armor on for those that with jump on me "BUT IT'S SO UNFAIR!!1!!11". Think about it. Buying CE shortens the time it takes you to make your 5*, since this is the prime objective of the game apparently. But.. if you don't buy it, you need patience. To make it yourself. That will also teach you how to play, and that 5* you will get will be much more valuable in your hands. Some learn after they get it, like me. But in the end, "who's best" does not depend on gear and who pays, like in most games. But on skill. I insist on this so much because.. I've seen it. I've seen myself die again and again, while someone in gear as good as mine had no problem.
And the gameplay is simply amazing. I really really like it. Of course, it has it's bugs and could be polished here and there, but hey the game is just a few months old. The art is .. really really impressive. The wide amount of armors and weapons too. On the technical and gameplay part, I can only say I'm impressed and it has an amazing potential. If it reaches it, that depends on the player, as I said so many times, on skill. That's how you can enjoy it.
To sum it up, Spiral Knights is not a game meant to be played continuously, and "finished" (reaching endgame gear) soon. You need to play it every day as much as you can, and enjoy it. Make friends, sell your loot in Haven, learn about how the game works. There's so much to learn about this game. And you can't do that by mindlessly grinding it. I think this is the most.. amazing mmo I've played. Because of the CE system and how it forces you to take the game slowly, and not rush to get endgame gear. Even though it is frustrating in the beginning, it's good for you. Unless you're a hardcore gamer that plays games for a few days then trashes them. This is not meant for you. I still have a lot to learn about it myself.

I made this pretty long and filled with personal experience that I don't think I can call it a review anymore. But I hope you get the idea and what I'm trying to say anyway. The reviews I read till now were filled with complaints about the CE system. I tried to focus on the actual gameplay experience.
And sorry for any typos that I might have made.