I have soloed characters to the level caps in WoW, EQ2, DCUO, LOTRO (though I have yet to catch up with the latest increase), and now Rift, so I'd suggest that I have a fair amount of experience with solo PVE play. Unfortunately, I can't recommend Rift all that highly in this department.
There's no way for Trion to balance content around all possibilities in the soul system, but any of the four DPS Cleric souls paired with 10 points in Justicar can chain-pull 3 mobs at a time with limited to no downtime or consumables. (I didn't even realize there were drinks I was supposed to be purchasing and consuming until someone mentioned how many they consumed on a dungeon run.) The game's zones are extremely lengthy and linear, so there's limited opportunity to push the envelope on better optimized solo builds by attempting more challenging content.
Meanwhile, the game's exp curve is inexplicably weighted in favor of killing mobs over completing quests. If you have rested exp, you will get significantly more experience for killing 10 rats than for riding halfway across a wide zone to turn in the quest to kill the 10 rats. Quest reward gear is generally much worse than what you can get at the same level from zergable Rift events. Overall, zones are pretty, quests and lore are reasonably well written, but overall the long and non-challenging quest grind feels the opposite of rewarding. Nothing about what I've seen makes me excited to work on the endgame solo daily quests.
The group flexibility niche?
My seldom-active Rift characters happen to be parked in Ferrel's raiding guild, Iniquity. Having seen my level 50 achievement notice in guild chat earlier that evening, the guild invited me on a farming run that very night. The group had some empty slots in an excursion back to farm the old River of Souls instance for raid currency etc, and they figured there would be unclaimed loot that could be handed to a blogger/tourist.
|Telhamat, with her new hammer|
Healer has to sign off? No problem, the tank will go heals and a DPS will switch to tank mode. Freshly dinged 50 who can't hit anything due to lack of gear? At least I can switch to a healing role and contribute somehow, since heals can't miss. Not enough players to run this zone? There's a smaller one that still has some tokens and loot, or the even less structured outdoor content.
None of these ideas are original or even that impactful individually. Taken collectively, though, I'm starting to see why this game seems to draw the older-school crowd from the days when MMO's were more of an activity than a game.
I'm actually not done with Rift just yet - I happened to snag a very good deal on some game time earlier this month. It appears that the biggest thing I need to do with this time is to stop trying to solo. I have more fun in this game when I play as a healer than as a DPS (perhaps in part because I have built a Purifier that heals a lot like my WoW mage does DPS). Trion will take my money as a solo MMO tourist, but they will never hold my attention in that role because that's just not the direction they have chosen to take their game.
In a lot of ways, Rift is the exact opposite of the direction I'm going as a player - subscription in an era of non-subscription options, group-friendly when that does not fit my schedule. The fact that the game makes me at least interested in trying it anyway suggests that they're doing something right.