I've got a Blaze VGA adapter and it's not particularly reliable. You need to use a special boot disk to force the PS2 into VGA mode. It's this twiddling of the graphics chipset which is what is flakey. Some games like Getaway have VGA mode built in so you don't need the boot disk.

Quality of the actual adapter hardware isn't that good either. I use one because my LCD doesn't support sync on green which means I can't use the proper Sony VGA cable.

Some games just don't work at all or they have graphical glitches. It's especially annoying for FMV since most of that is written to be 50Hz when PAL and VGA is 60Hz which means you get out of sync.