G.A.S.L.I.G.H.T. comes up fairly often as a game suitable for solo play so I won't belabor the point.
I just want to note the reasons why I believe it does:
1. Turn Sequence - G.A.S.L.I.G.H.T. uses an activation deck to randomize who is going next. Each unit (vehicle crew, infantry, cavalry, artillery) and unattached main character gets 1 card in the deck, heroes and units lead by heroes get 2. Thus the non-player side may get a run of cards and trounce your troops and there's nothing you can do to stop it.
1b. Each unit can only do ONE thing on their card: move, shoot, charge or reload. This obviously is the case for multiple players as well. However, I think it goes a long way towards making the solo game interesting. Waiting for the card you want to come around can be brutal! Watch as your plans crumble before your eyes!
2. The morale results - see the last post. As a solo player I like when the rules take things out of my hands. When the King's Regiment scatters across the table, I swear under my breath and send the officers running after the men. It's an added challenge. Combined with the uncertainty of when they'll activate next, it forces the question, "How am I going to recover from this?"
3. The main characters - It seems to me solo players more so than those who game with others, tend to emphasize the narrative aspect of their games and the exploits of individual characters in particular. Having characters on the table makes it that much easier to tell a story - at least for me. Sure, you can add character figs to any rule set, but having them a part of the rules as written encourages the creation of stories - without having to fiddle with the rules.
Now, Soldier's Companion might do this better as it's a wargame written to accompany an RPG, and every TSATF write-up I've ever read includes at least a commander as a character, so this isn't unique to G.A.S.L.I.G.H.T.
3b. Saving rolls - This is by no means uniquely advantageous to solo play, but it does support story telling. Saving rolls add something of a pulp feel to the game - brave men and women who keep fighting long after others would have quit the field. Or perhaps it just represents that they are individuals while the extras are some nebulous quantity. Or maybe it's just that Lady Luck smiles on them. In any case, it's a small thing but being able to tell a continuing story about the same characters is something I find makes my games more enjoyable.
Next up: The wrap up including what's "wrong" and any other bits I meant to mention but didn't.