I totally agree you.
It is not a Fallout indeed : however it IS a great game.
The world isn't the one of Fallout, and the game type is far from Fallout one. It is more tactic than RPG oriented. It has not much of an RPG at prime look BUT, as the world feels close to the Fallout one, you may enjoy the epic saga of the Brotherhood of Steel that Fallout Tactics features.
A very good game. Very well realized : it is beautiful, it really puts you into the mood as other Fallouts were able to do, and it's a very good tactic game.

It isn't a simple question though. Asking people what a game is to them is like asking an artlover to define his favourite artworks. You're rarely gonna get the same answer from two different people. I'm not comparing videogames to art, but I believe that artlovers are as different from eachother as gamers are, even if their favourites match every once in a while.
For me it was the fact that both Fallouts were so stimulating in the totally uncensored, completely hopeless, bitter and cynical world they portrayed, full of people gone insane from the events that occurred, of course coupled with the sense that you were a real actor in that world, a hero even. Or a bastard. Either is insanely appealing to me. It's one of the very few games where I completely lost track of time and "came to" after an entire day of playing.
I actually think Borderlands got a lot closer to capturing the art and the feel of Fallout than Fallout 3 ever did. Neither game had a real story to go on or a lot to offer in the way of characters, but Borderlands had teeth and it was harsh, where Fallout 3 was a relaxing stroll through suburbia full of tame everyman characters, minus the lawns and the kids in hiphop clothes.
Anyway, Fallout T was a-okay, but it was still an unrepentant tie-in.

Do you know, in this thread about Fallout Tactics this is the first post where the words 'Fallout Tactics' have been used! :)

For me, a "true" Fallout is all about what Kaotiker said. "stimulating in the totally uncensored, completely hopeless, bitter and cynical world they portrayed, full of people gone insane from the events that occurred, of course coupled with the sense that you were a real actor in that world". He said it brilliantly so there's no point restating the same thing. So I guess Fallout fans CAN agree. To extend a bit, it's a lot about exploring this world, interacting with it in different ways (remember the dialogue for a low intelligence character?), and getting to know (and love) its lore.

Because, I must say, Fallout has one of the greatest pieces of lore I've ever experienced. That is why F3 by Bethesda didn't work. Not to say they can't come up with touches of genius every now and then and that the engine is bad. I just hated the way they dismissed the assistance of ex-Fallout dev team members, and it really showed. Fallout 3 was a 3D Fallout Museum of sorts, with mostly bland story, characters and dialogue, with little sparks of genius left in the side quests and locations. What many newcomers enjoyed in the main quest was way too bombastic and out of place to fit the Fallout lore. Fallout isn't about the "big deal", it isn't an "epic saga", but a huge, brilliantly painted veil that encourages you to stare at the tiny details that happen to fit so well in the whole.

At least Obsidian got it right with New Vegas. So right, I wish they had developed the initial Fallout 3 as well, with Bethesda just working to improve the technical side, engine and such.

Therefore, not being an RPG, Fallout Tactics cannot be a "true" Fallout, because as a TBS it lacks the possibility to develop the core elements that made F1&2 the legends they indeed are. It's a gorgeous, tight and challenging Fallout-themed TBS and worthwhile for both TBS and Fallout fans, since F1&2 had turn based combat and it's unlikely that any of their fans didn't enjoy it.

Opinion on what makes Fallout a Fallout is individual, for me it is simply the universe. So, for me the TBS is Fallout as any other. Why we cannot live the adventure in Fallout universe from another point of view? And if they make racing game from Fallout universe (something like Fallout Racer :)) ), for me it will still be the Fallout (though I hope i will never see anything like that :) ).