Some of these ideas may have already been mentioned. I'm sorry, didn't mean for it to be this long.
I think Death Mages, Necromancers, need some more work. Normally when I think of Death and Necromancing, I think of creepy and scary. A pixie/sprite is not scary. I understand that it is your first spell and it's not suppose to be the coolest or best, but a pixie? Surely they can do better than that. Especially since other schools are summoning giant snakes and beattles. Maybe change the pixie to a large spider, or a lot of little spiders. Just something besides a what it is now. The ghoul is nicely done. The sounds and the way he "rips" out the enemies life with his shovel. But, the skeletal pirate.... That is something mages fight at level one.... and now I'm summoning it has a rank 5 card? Doesn't seem right, or even fair to a death mage. Maybe make it something comparable to the other cards at this point so that it looks like a spell you can admire like the other ones. Like, a large skeletal hand that slams into the opponent or something. Anything but a level one monster. The banshee sounds like a man when she/he comes out. Looks like a women though. Maybe change hi/her laugh. Maybe even up the damage on a death mages damage cards. The banshee barely does anything compared to other 3rd rank cards. I know that Death Mages aren't suppose to be the damage school, but maybe just had a little more. Death Mages are doing the same as Life Mages still! I think the Death Mage would be able to do a little more damage than a Life Mage. I know that Death Mage has damage spells that drain life, but Life has spells that heal a lot of damage. Way more than a Death mage could hope to gain. So, a way to balance this out would be give the Death School a little, tiny, damage buff to their cards that don't heal them. Sorry for this long rant on Death Mages.
Maybe make more than one arena. And make them so that you have to be a certain level to enter them. Like a "Level 1 - 5" arena area. "Level 6 - 11" area, and so forth. That way when I enter a battle as a lvl 15, I won't be fighting lvl 2's. I always pass when this happens, and just wait out the battle. I know I can flee, but still want to fight. So, making more than one arena with level caps would solve this I believe.
This has been said before, but the chat system. :? Everyone knows what I'm talking about. I understand many words that can't be said, but there are many words that I can't say that are just common words that everyone uses. Maybe add more words to the dictionary, being that younger players can't access the text chat anyways. Not asking to add words that we know are bad, just common words. And, it would be nice to have numbers. The words we have to use to get around are ridiculous.
That's all that I can think of right now. But, in my defense, this game is one of my favorites. I have played many games, including World of Warcraft and Everquest 2. This game beats WoW by a long shot for me, the community is nicer. And, comes close, if not tied, to Everquest. But, this game's monthly subsciption is way better. And, love the gameplay.
I have played WoW as well, and yes, I am now glad and without regrets that I deleted my account characters and quit that toddler playground of a game.
I am not sure how long you have played a Death wizard, but knowing you got the Skeletal pirate, you must be at least at Krokotopia +. Death wizards have their perks. True, they are not very powerful, but they ARE a bit more powerful than life. The varying damage might of course make it difficult to see right away. Also, accompanying their higher damage, Death wizards do get a decrease in accuracy.
With the training points you do get, you can train for Satyr, a fairly high powered healing spell that any class can get. So, ontop of drain spells and Pixie, Satyr, and the 3-pip healing spells only Death students have, monsters can have a very hard time finishing you off.
As for the visuals, I have not really thought about it much, but I would have to say that the level 1 Pixie spell looks pretty good. It is a "Dark" pixie. :P As for the other spells, while they could have been made more scary (very true) look ok to me though, I never really had any issues with them.
Also, Death spells (that drain health) penetrate absorb shields. You can use that to your advantage when someone is trying to block your attacks. No other school can do that. Unless of course, they trained in the Death school itself.