Rune: Halls of Valhalla is both an expansion pack and a stand-alone title. It contains a large number of new Deathmatch, er, Runematch levels, two new online play modes and maps to go with them, and a number of new player models and skins to enjoy.
Unfortunately, that's all that it offers--no adding to the single-player experience, which was by far the most enjoyable part of the original Rune, no large collection of new and crazy weaponry. Just new levels, playmodes, and skins. And since the game has no Unreal Tournament-style bots, you're stuck playing Halls of Valhalla online, or not at all.
The two new playmodes are Headmatch and Arena. Headmatch is reminiscent of Capture the Flag, only in the Rune universe. Every player is on a team, and attempts to score goals for their team while keeping the others from scoring. The method of scoring goals is decidedly unique, however--you must lop your opponents' heads off, and then throw them into a sort of 'collector' to get points.
It's a neat idea, and it actually makes for some entertaining gameplay, but it never really feels like a heavily team-based experience. You'll see people running around the maps like crazy, slashing at each other, occasionally scoring points, but there's no sense of attacking in a concerted effort--it's simply 'us versus them', and whoever gets the most points wins. While it's entertaining, I prefer my team-based mods to be a little more, well, team-based.
The other play mode, Arena, is both more interesting--if you're playing it--and a lot less interesting, if you're waiting in line. Arena lets you go one-on-one (or two-on-two, or whatever) in an arena, fighting to see who are the superior combatants. The winners stay in the ring, whereas the losers are booted out. If there are enough people on the server, you go through something of a round-robin routine, where you have to wait your turn.
While the battles themselves are fun, and more focused than the somewhat slapdash Headmatch mode, the wait for your turn can be interminable, and quite simply just isn't fun. Some maps have a number of things you can do while waiting, but it's still keeping you from actually playing the game, which is a definite no-no in online gaming.
Another major problem with Halls of Valhalla--one that, unfortunately, will be self-perpetuating--is the fact that there are almost no servers online playing the game. At last glance, I saw three or four Headmatch servers and about ten Arena servers, nowhere near the numbers of a more established multiplayer game. Chances are good that you won't find very many opponents to play against, which is a shame.