You can get it in the repositories be installing "wesnoth".
The graphics are well drawn and it has the sense of a game that you would pay for. There are loads of different character types and each one has a different image, they're not just edited with different colours.
Wesnoth has great level designs, despite being limited to a hexagonal grid
As a turn-based strategy, Wesnoth has lots of different factors in gameplay. Units level up, and have various statistics, multiple weapons (which also have lots of stats). Playing in the night changes your units abilities, or playing on different terrain. At first it can seem a lot to get your head around but it really makes playing more fun when you have to review all the stats before you make a move. It's also got a battle calculator so you can predict the possible outcomes of each battle before you attack.
Level, HP, XP, MP, Defence, Allegiance and weapon stats all to consider
Wesnoth has a extensive single player campaigns and and multi-player over the internet, so it doesn't get old. Single player will last you a while if you play a few hours a day and once that's done you can have countless battles over the internet (which is even more exciting, in my opinion).
There are 15 campaigns, most with over 10 scenarios
In conclusion, Wesnoth is an amazing game which, being free, is something you really should try because on Linux it's one of the best games available.