Solo legendary is more of an annoyance that it is difficult. It's very tedious, of which I don't mind, however it's the situational disadvantages I'm put in that make the campaign more irratating than enjoyable.
Was near the end of mission four last night, where you have to hold the area in front of the door while Cortana hacks into it. Naturally, all of the supporting Marines die long before you get to that area (regardless of what weapons you give them), and the weapon caches are all near the front of the door, which is in a completely open area, where all the enemies tend to converge. I was forced backwards into the level to camp in an outpost under the cover of some foliage on a tree branch, where I picked off Crawlers before I ran out of ammo. The blessing on that level are the turrets, which manhandle the Knights (granted you get rid of the Crawlers first). The worst part is missing a Watcher and having them spawn in more Crawlers and revive the Knights while you sit there helpless because you've run out of precision weapon ammo and all you have is a half-empty Boltshot and a Supressor.
The amount of enemies and the placement/selection of the weapon stashes on that part of the level are super frustrating, and the feeling I got after beating that part was more of a "FUCK YOU" rather than a "FUCK YEA!"