Although I never was a truly skilled player, I always enjoyed to complete a campaign, go play on the official multiplayer server or just read the forum, which actually is a great resource of strategy tips, ideas, suggestions and debates regarding playability or improvements.
Wesnoth 1.4.5 running in window mode
The development is more alive than many other open-source projects, and it is done in an open fashion on the forums. The developers are implicated there and often talk to other players and eventually listen to suggestions and add them in the development version. The stable release (currently 1.4.x) benefits of updates every few weeks or so, while the development branch (1.5.x) is also put out to the public for testing purposes.
Many add-ons are available: campaigns, factions, new maps and eras. The game comes with six default factions: Rebels, Loyalists, Drakes, Northerners, Undead and Knalgan Alliance. Each faction benefits of its own units available for recruiting; and each unit has special traits and abilities. The battle between players takes place on a hex map, and each hex can provide different defense resistance, depending on the terrain and the type of unit standing on it.
Maps included by default are well-tested and some of them gained real popularity in time due to either playability or situations which can evolve in time. For example, an interesting map is Isar's Cross, a 2vs2 map which although is small-sized, can make the game evolve into very interesting positions, where the whole game can depend on one unit, a village, or just a lost tempo during the day/night cycle. I've seen players who played this map for so long that they play it like chess: well-known combinations and movement rules for X first moves, depending on own race and the enemy's.
Of course, the most important part of the game is that it randomises a battle's result using the chance to hit, so you can't be absolutely sure what the result of a battle will be until it's over. There are strong debates back on the forums, with some players complaining this system may not be the best, but in fact it's the only thing that keeps the game entertaining. After all, a skilled player will always beat a novice player, even if the latter is 'lucky'.
Online playing is a real pleasure. There are always games which you can join, or eventually observe. Tournaments are organised often too, via the Wesnoth Ladder website.
Another aspect I just love is how players gather on the forum and discuss a situation or issue, accompanied by various replays, suggestions solutions or helping a new player who can't beat a scenario.
The game also provides a complete help system for gameplay and each unit. This is the basic stuff you'll need to learn in order to gain experience and skill. Of course, it needs time to master this game. I play it for maybe 2 years or so (version 1.0.2 if I recall correctly), sometimes occasionally and sometimes for a couple of days non-stop, and I still can't say I qualify more than medium-skilled. The second way of getting help is via the Wesnoth wiki, which contains invaluable information on playing the game, together with complete guides. I already mentioned the third way, which is the forums. Don't forget #wesnoth @ Freenode if you use IRC, you can chat about game aspects there too.
Isar's Cross map
Being actively developed, this game always gives me the impression of constant movement and improvement, like it's 'alive'. Release 1.4.x brought new artwork, a new and improved interface. I'm talking about real improvements: scrolling maps is gives a smooth impression, menus now have sounds when clicked, the game interface is maybe five times faster than 1.2.x, several units are now animated, transparency effects for game messages windows, and these are just a few of the great new features. New official campaigns have been introduced, and plans are to increase it even more in the next stable release.
Waterloo Sunset map
You can run Wesnoth in both fullscreen and windowed mode, using the default shortcut Ctrl+F.
Playing Wesnoth is maybe one of the most awesome gaming experiences, at least it is for me. I like to see this completely free, community-maintained project getting more and more fun and polished with each new release.
Download Battle for Wesnoth
Compiling from source in Ubuntu 8.04 and Debian Lenny
You can compile and install the last 1.4.5 release easily on both Debian and Ubuntu.
Edit your /etc/apt/sources.list file as root and make sure you have a line which starts with deb-src. Ubuntu users, make sure to precede the following command as root. For example, on Debian Lenny the line in the sources.list should look like:
deb-src ftp://ftp.ro.debian.org/debian/ lenny main contrib non-free
While on Ubuntu 8.04 Hardy Heron:
deb-src http://us.archive.ubuntu.com/ubuntu/ hardy main universe multiverse
Save the file, then update your packages list (also as root):
You will first need to fetch the dependencies as root:
apt-get build-dep wesnoth
Next, download the source tarball from the official website, here, uncompress it using:
tar -xjf wesnoth-1.4.5.tar.bz2
Then change the current working directory to wesnoth-1.4.5 and issue the following commands:
The last one as root. You can pass the ./configure script the prefix parameter, e.g. ./configure --prefix=/home/your_user/usr/, and then make install as normal user if you like. This should be all.