Using a program called HalfMapper, gzaloprgm posted a nice gallery of classic Counter-Strike 1.6 maps with the camera angle set to isometric view. It no longer looks like a competitive FPS, but like a classic X-Com game.
I can imagine myself playing a turn-based strategy game on these maps. Here's cs_italy, de_dust2, de_train and all the other old 1.6 maps from above:
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