I enjoy the effort, but I want to voice the concern of making sure the health window, combat window.. any window in general, doesn't get too big.
You want to keep things nice and compact, so the screen doesn't feel cluttered.
You also don't want to distract people with the UI.
The first thing I think was unnecessary, was how much bigger you made the minimize and X buttons.
Sure it looks nice, but I think it is a bit unnecessary, and it will get in the way later on when players have tons of backpacks and have to go through stuff.
Even when minimized, they will take up more room.
It is also a bit too colourful for something that is so mundane, but thats a bit of a personal opinion, and not really that objective.
I know alot of people will jump down my throat for this, but I don't like the health bars.
All the lines(bars) over the bar, the thin text font, and the fact that the numbers are not inside, seem to be working to distract me from actually seeing the real information I need.
When I look at my health bars, it is normally because I am either low on mana, or in the middle of combat and don't want to die.
On real tibia, the actual bars are small, and the numbers on the same plane, so it's easy to correlate them.
On the OT Client, the numbers are inside of the bars, so I see it right away.
With these health bars, my eyes jump all over the place.. there are little bars all over the health bar for no logical reason..
The little bars should be placed at important levels of health and mana, like at 75%, 50%, and 25%, so not only can it look nice, but it give you the information you need, and quick.
The text font is all thin and weak looking.. the numbers kinda blend in together.. which is not a good thing, you want each number to be bold, strong, and defined, you want it as vivid as possible, because no one wants to die because they had frustration from a bad choice in font.
But the biggest problem is, that my eyes have a problem finding the real information I need, the raw number of my current health or mana..
the real information I need is kinda pushed away underneath, which can be really annoying when you are playing in the middle of combat, about to die, and you NEED that information without thinking, you don't want players eyes jumping all over the place.
So my suggestion for that is to work the health bars to have the number of your health either be inside the actual health bar, or next to it, on the same plane, in a nice bold font.
The Combat Bar looks nice, artistically it looks nice, and the frag counter, after seeing it, is a MUST from here on out, after you see a real good idea, you never want to go back. haha
Only concerns are that the box is a bit too big, the big skull looks, weird.. and I think you should put back in keep-distance for a follow command.. the old feature where a player would keep 2 squares away from a target at all time.
I hope you take my post as actual criticism, and not bashing, as I want to see this server succeed, and I enjoy seeing someone make the effort that is needed to make a good server/game.