>>96146080
Moderately so.
Good:
Some published solo adventures (mostly 3rd edition) and a few fan-made ones too
Reaction table determines NPC attitude 'fairly'
Combat system well suited to small number of combatants
Generally simple to create broadly-competent non-specialised characters
Few rules require information to be hidden from players
Bad:
System not explicitly designed for solo play so numerous minor rules / gameplay elements written with the assumption that GM is available
Lack of random tables for spontaneously generating game content (although a few good ones such as Dungeon Fantasy's treasure tables)
Few pre-generated NPCs
Much of the fun of PC design and gameplay comes from cooperation (and sometimes conflict) with other PCs

Overall, I'd say it's about as good as you can hope for from a game not designed for it.