Now I clearly cannot speak for everyone, but my favorite levels are usually 5th to 7th level. Thing is, while I have played 5th level BX PCs before I don't think I've ever leveled up a PC to 5th level before. Those other PC's were higher level for one-off games and that is a different animal than "growing your own" straight-up from 7 x 3d6 down the line.
Now for an Enchanter that means I get to finally cast a 3rd level spell and get to cast a total of five (count 'em.....FIVE!) spells a day. My Enchanter (I should totally rename his sorry ass to "Tim") conceivably could cast Lightning of Fireball, assuming he knew those spell. Instead he knows Water Breathing.
Water Breathing.......sounds kind of crappy, but after reading the spell it is pretty bad-ass, just a little limited in usefulness. I'm more excited by the fact he's got a captured spellbook with Dispel Magic, which might be far more useful.
Now I expect that most here get the nuances, but there is probably at least one person here that isn't familiar with the slower rate of level progression in an OSR/BX game. I think I've been playing this PC regularly for at least a year and a half. Now as a low-level support PC I'm not often in the thick of things, although I have had to step up a few times and save the day (usually through a fair bit of luck!). Thing is, and this is for the new guy, a 5th level BX Magic User is a lot more on par with a 1st level BX Magic User, much, much closer than the differences in pretty much any other edition of D&D.
My guy is still running the same to-hit charts and saving throws. The difference between 4th & 5th levels? 1d4 hitpoints (well, 1d4+1 for me) and a single spell, albeit a 3rd level spell. The jump to 6th level, only another 20,000 XP from now, gets my guy the 1st increase in saves and to-hit matrix, not that I really want to be making saves or engaging in more direct combat.
Yes, progression is much slower in an OSR game, BUT...and this is a major draw for me, that sweet-spot of mid-level gaming is a lot longer than in other games. Now that my PC has access to 3rd level spells, even just one (up to three if my GM's custom Bracers of Spell Storing can hold third level spells....but I suspect they are limited to 1st & 2nd level spells) can change the dynamic considerably....."can" being the operative word.
Again, for the not-quite-familiar, the flexibility, adaptability, survivability....hell, just playability of BX (OSR) Player Characters aren't so much related to the numbers gained through regular level progression, but through the "smart" actions of the players at the table, and of course a fair bit of luck. Now I'd LOVE to be able to take all the credit for "making it" to 5th level, but I have a whole party of players that are responsible, along with their PCs.
I know, I know.....for 90% of the readers here this is old hat and you've probably not even made it this far. Earlier this week I was reading about *ahem* another edition and my eyes glazed over at the prospect of making and leveling up a PC. Since it's a matter of public record that I like HackMaster and believe me that game has a complicated build/leveling process, but that shit is enjoyable and a completely different thing, so aside from this throwaway comment, I'm not going there.
I remember playing 3.5 and rolling up a PC, or leveling one, seemed to take hours. It took so damned long because if you did not optimize your build you were screwing your PC over and possibly your group as well. Now this was my experience and others might have different ones, but the simpler/easier choices of OSR PC creation & leveling up > complicated, "have to get it right" please read all the RPG books of the month-club to optimize later edition creation/level ups.
Now I'll probably loose my PC in the next couple of games....these things happen, but I'll just grab my 3d6 and be back in the swing of things soon enough.