I got an Acer Aspire One when they first came out. It's great for uni because I need to travel quite a bit and it's lighter (and cheaper!) than a big laptop.
I haven't tried running Half-Life on it, but somehow I have a feeling that it wouldn't work
I should probably try it anyway and see what happens.
One issue I have is that the default 3-cell battery only lasts 2 hours or so at full charge. This was pretty bad last year when I had a 3 hour lecture that was mind-numbingly boring and I had nothing to do for an hour after the battery ran out! You can buy a 6-cell separately, but it's not worth the cost in my case. Looks like the one you ordered has the 6-cell battery already though
They're good as long as you don't use it to do much. If you find yourself doing a lot of typing or other activities that may be hindered by the small size, it might be time to get something larger.