First impressions are something that's usually a deciding factor whether we're going to play all the way through a game or not. If we get turned off in those first moments of gameplay then it's safe to assume that very soon we'll be searching for another title. Being fun is the most important factor, yes, however sometimes you can't really get hooked till you're already several hours into the material. This is especially true for those more “complex” games, those that involve management, vast research and slow-paced advancement.
Let's take this to an extreme: Imagine you make a good-looking game with high polygon 3D models and nice dynamic shadows. A real eye-candy. We, the players, look at screenshot, find the look very appealing and want to try it out. We start the game, navigate through a mediocre menu screen, start a new game and then realise that the whole action is happening inside a small square window. The rest of the screen are, in fact, flat black panels with bunch of numbers and confusing colourful buttons. We press on a unit and it gets surrounded by a strong neon glow, while right-clicking it opens a whole list of one-word actions with a scroll...
Although I imagine there are people who would actually spend some time figuring out the ups and downs of such a mess (if you're such a person, I salute you) I hardly believe anyone would find it appealing no matter how enjoyable the rest of the game is. My point is: A good user interface can drastically change our outlook on a game. It has the power to make an average game extremely satisfying and, if done badly, vastly diminish a high-end game's value.
For the record: EVE Online doesn't have it as bad as some other interfaces out there.
It could've still been much better though... Just sayin'
So what makes up a good UI anyway? Dynamic panels? Aesthetic contents? Functionality? It's safe to argue that all of these factors are equally important. It does vary a little depending on which platforms the game is developed for, but the same goals always apply. Making a beautiful yet useless panel is just as jarring as making one with every possible command which makes your eyes bleed whenever it pops up. Not to mention when using those colours that obviously jut out...
Referring to that quotation from the beginning: a good user interface is unnoticeable. It melts into the rest of the game just enough to help the player enjoy the experience and not drive them away. If a blocky panel is the first thing people notice when entering the game for the first time, then you've probably done something wrong. If they didn't notice the panel but spent an hour scouting the screen and still have no idea what to press next, then once again you've botched it. Among other things: keep in mind the variety of display resolutions people will be playing the game on. Nobody likes having half of their screen covered in a panel, nor does anybody like zip-zapping from one side of the monitor to another just to press a single button. Hotkeys are no excuse for a lazy interface design.
All in all, do consider what your user interface looks like. If your game is still in the works, a decent starting interface will help show you're serious about making the game look good. If it's nearly done, ask people to evaluate. It shouldn't be that difficult to come up with a decent UI, right? Just give it some thought.
