First of all, this is a GAMING mouse. If you are using it for something other than gaming, then it isn't optimized for you. For example, there is no side scrolling and the mouse is corded. Corded is a good thing for games, because there is lower latency, no need to change batteries (having to change a battery in the middle of a game could be absolutely disastrous!) and you don't have to worry about interference if you are at a LAN party. If you are working in the office or surfing the net, cordless is nice because you get the obvious benefits of being tether-free and the disadvantages are insignificant--you don't care about 100ms latency and if you have to change the batteries at some point, the spread sheet will be perfectly happy to wait for you while you do so.
So, having said that, let's look at this as a gaming mouse. There are the normal left and right buttons and a clickable scroll wheel (as previously noted--no side scroll if your game would benefit from that). There are also two buttons by your thumb whether you use the mouse left- or right-handed... which means there are also 2 buttons by your ring finger... which I've got to tell you... I can not find a comfortable way to use those buttons. I see they are going for ambidextrous, and that's cool, but for all intents and purposes, those 2 buttons are going to be pretty unused. Finally, there is another button just below (closer to your palm) the scroll wheel.
After you go online and download the SteelSeries Engine (the product does NOT come with a CD), you can assign actions to each button--these can be either recorded Macros, or you can specify an application to launch. The macro engine seems pretty complete to me--you can record keys, mouse clicks and combinations thereof (like CTRL+SHIFT+Left Click). You also have the option to include time delays. It looks like there should be a way to make modifications to this without having to re-record your macro, but I haven't figured out how to do that yet. No big deal... either way. Since you can record rather complex macros, you could assign an unusual and difficult Macro to the ring-finger keys and then maybe get some mileage out of it, but they better not require the pointer to hold still because using those keys, I ALWAYS move the mouse at least a little, even if I'm trying not to... very unnatural...
The scroll wheel and the "Diablo" logo on the back of the mouse pulsate red. The engine allows you to control how fast that happens (or disable it completely). The engine does NOT allow you to change the pointer speed. You can change the polling rate between 125 and 1000 Hz, but the speed seems to stay pretty constant for me. That's not a big deal, though-- you can use the Windows mouse controls for that.
The mouse uses a laser tracking system and seems to work flawlessly, even on my glossy wood desk.
Personally, I prefer a mouse with a little more heft to it, but this one is perfectly usable. Even though it is lighter than my other mouse, it still feels solid.
So why only 4 stars? Several times while I was messing around in the engine, my left mouse click would quit working and I had to unplug my mouse and plug it back in in order to keep using it. This only seems to occur when I'm playing around in the engine--not during normal use (at least not yet). In fairness to the mouse, I have drivers for several other mice on this computer and they may be interfering with each other, but all the same, I don't have these problems with any others and the left mouse click is kind of a big deal. If it did it outside of the engine, I would have to drop this down to 1 star since losing that functionality during a game (remember, this IS a gaming mouse) would only be slightly better than having the batteries die on you. So far, though, it is just a quirk that will only contribute to the loss of a single star (along with the awkward button placement).
===== UPDATE 12/2/2011 ======
A friend of mine was invited to use the Diablo III Beta and has been playing it for some time now. He has beaten it using all but one of the rolls. I let him use this mouse for a couple days. At first he wasn't sure how he felt about it because the button by your pinky finger is (by default) tied to you potions. As I noted above, this button is really in a poor place--hard to use and easy to click accidentally. He accidentally used several potions without meaning to during the first day he played with it. Once he got used to the mouse, however, he said it was a great improvement over his other gaming mouse (
Razer Naga Epic Gaming Mouse) because this one was better optimized for this particular game. Now that he's been using it for about a week, I'm pretty sure that when I ask for it back, he's going to run out and buy one for himself. NOTE: I asked him if he has ever had the quirk I mentioned above with the left button not working and he said it has not happened to him once.