I think it depends if you like RTSs. If you do, I recommend the first one at least, as it is a very good RTS. (I can only speak from a Single Player perspective.)

The graphics are excellent. The production values are very high - good cinematic exerts from the trilogy; good voice work by some of the cast; nice sound etc. The combat is more tactical than most RTSs: there is an element of "rock-paper-scissors" and units, especially heroes, have special attacks or spells that add variety. The campaigns are pretty linear - really just a sequence of maps, no Total War style strategic level with proper strategic decisions (BfME2 does have more of that, apparently, but it sounds very flawed). There are a few absolutely terrific set piece battles. Helm's Deep is a standout, but Minas Tirith is excellent too. It is hard to believe a game can reproduce them so well. They are epic and have something of a total war feel about them. There are some "RPG" elements - you have a core set of units that gradually expands; they can get upgrades and go up levels of experience. If you like Tolkien or the movies, there's a lot of fluff there - all the units and characters you expect are there (you even get to play Sam facing off with Shelob).

From all the above, you might think that it is a brilliant game - rather like Total War or the early Panzer Generals (which I loved). But it is still an RTS. The combat is just too fast. Think Rome Total War running at about twice the speed and no meaningful pause button. I just could not enjoy it much, either tactically or from an aesthetic point of view, because it was too hectic. The base building side is also pretty phoney and an RTS cliche. The other irritant was that because you have a core, you don't want to lose any units but in the chaotic combat it is so easy to lose track of one and find it is gone forever. (You basically group units together and launch them as a blob on another enemy blob of units). That tends to lead me to reload, again lowering the fun.

I got pretty far in the good campaign - up to the Black Gate. But I did not finish it and don't really feel the urge to go back to it. I just don't like traditional RTS games and should not really have bought that one.