I'm not a fan of energy weapons in general, although I did use Elijah's LAER and jury-rigged Tesla cannon a bit. I didn't really find the holorifle that good or enjoyable, even after modding it. Then again, that might've just been a result of Dead Money's HP bloat since I never bothered to try it in the main game. I guess it does do a pretty nice amount of damage if you look at the numbers.
I found the Holorifle (even on extra-hard, which reduces the damage you do, I believe) to be very effective in DM. One or two shots to any limb and they're down for good. Maybe helps that I pump energy weapons, and take the related perks - especially vigilant recycler, which (with GRA) gives you optimised MF cells, which have a bonus to damage and to DT reduction. But each to their own - the other weapons in DM were underwhelming. In fact, standard guns in general weren't served that well by the DLCs, except for Christine's COS Sniper Rifle in OWB(overpowered) and A Light Shining in Darkness in HH(which I like).
OWB also gives you some pretty insane perks, although you can fortunately un-choose them at the end of the DLC. Still, I think the difficulty curve is more or less screwed anyway unless you pick the Logan's Loophole trait.
Yeah, although the existence of DT, among other changes, makes the difficulty curve much better than FO3's, where the high end creatures (SM overlords and such) were all HP sinks with stupid Damage resistance - not difficult to kill, but really, really boring. Proving again that Bethesda doesn't know how to make a non-broken levelling system. As if Oblivion's wasn't bad enough. FO3's VATS with its insane damage resistance, combined with FO3's Grim Reaper's Sprint, was basically a "fuck it, you got to level 20, you can kill anything now". Pretty hard to do a high level difficulty curve that doesn't start to get stupid, but especially hard when you're building on Bethesda's clusterfuck. At least perks don't come every level now, and it's harder to max out every skill (fuck you, bobbleheads). And plenty of Bethestards complained about the slow perk rate.
Overall, I agree, though. Limiting max level and slowing progression is key to getting the most out of NV. The problem with Logan's loophole is that the chems are very, very useful, and addiction/ length of effect are the major drawbacks of something like turbo. Without that, you run through the game sniping everyone from a mile away with steady, and taking down sentry bots with tire irons using slasher and turbo.