I guess it all depends on what you want out of XBLA. For some theres game on there that bring back memories and may not be able to get again on any other system (such as Frogger and Dig Dug and Root Beer Tapper), these 400point games will probably look a bit crappy to people who are new to them, but for those who used to spend their childhoods in the Arcades spending all their pocket money on this kinda thing will appreciate it more.
Then theres the completely new arcade games that have been built from scratch and cost around 800points, these are the games I prefer personally. They're good for a quick bash whenever I fancy a change from racing or shooting, they're refreshing! but thats only my opinion.
And last theres remakes of more recent titles such as Lumines, Exit, GripShift and RezHD etc. Personally I've played the originals of these before they arrived on XBLA (Lumines, Gripshift and Exit on PSP, RezHD on Playstation 2) so I knew what to expect. I guess if you don't have a PSP then this is another option if you wanted those games, as for RezHD, well the original is incredibly rare on the Dreamcast and Playstation 2, we're lucky enough to still have it on Playstation 2 and wouldn't sell it for the world!
It all depends on what you want out of a game, if you think they're a rip then don't buy them (theres always free trials of every single one to try before you buy though).
I love em!