Overall Total Annihilation is a really good RTS to even just play with A.I.

User Rating: 9.2 | Total Annihilation: The Core Contingency PC
Total Annihilation was like my second computer game I've ever owned and it has been fun playing it it many ways even though its not using the newest in RTS 3D graphics its still has a straight forward game play that you can always have fun playing. So this is probably another addition to the must have RTS that is just addicting. However its hard to find TA on sale anymore which really sucks but there are very few places actualy selling TA and all of its expansions if you search hard enough or just download the demos off this site.