Yesterday, after my previous post, I played two more credits and confortably got the 1cc.
The game is actually fairly easy (but not on Hard, more on this below) and I'd rank it about the same as the Famicom games in terms of difficulty. Most of the damage taken on that first run was from getting used to the controls (always ended up blocking when trying to jump) and from trying to be fancy with the block move which, to be fair, is quite fun to (enemies getting pissed off when you throw them is an amazing detail). I also had some trouble with the twin kung-fu guys that appear a few times; kicking these recklessly tends to end up badly.
What puts the game on the easy side is that enemies are very vulnerable to close range attacks -- much like in the FC games. If you score a knockdown, then you simply get very close to the enemy's feet and do a combo as soon as they get up; I enjoy PPK. And to score a knockdown, all you have to do is perform a late/meaty jump kick, which works even against the tougher enemies that block (that is, jump towards them and wait until they stop blocking before kicking). This trivialises much of the challenge, even the last boss.
The weapons are nice, most of them returning from previous games (the boomerang is pretty amusing) but the nunchaku must be given a special mention because it is fantastic; you can take down anyone with it with little effort. Of course the levels are divided into separate sections so you can't ride with any weapon until the end.
More importantly, in my opinion, the game ditches most of the platforming and all of the cheap sections that haunted the previous games, leaving only the core beat-em-up experience. It also retains some of the constrained sections (depth plane-wise) present on the FC games, though none are strict 2D (nor as hard).
I was a bit disappointed with the last boss, though; he's not much different from the usual tough enemies.
I didn't want to post without at least trying Hard mode, and besides the usual increase in enemy aggressiveness (and maybe damage output?) it has a major difference to Normal mode -- enemies will block anything you do at close range. It requires a different approach to the game which I find quite nice (at least it did for me).
You can still score knockdowns with jump kicks, but the meaty jump kicks no longer work because enemies will keep blocking. Approaching them upfront can work, but is dangerous, so I found it best to throw a punch, move up/down slightly, throw another punch and hit them with a roundhouse while they're stunned (the one perfomed by holding either L/R shoulder and pressing kick). I've never seen this roundhouse fail, but the standard combo ending kick/roundhouse fails quite often.
Once they are down, there is something else you can do trap them. Instead of keeping close, move away just within kicking range, and perform a two-hit-kick as they get up (Down + Kick) followed by a roundhouse (R/L+kick). If the low kick hits the high kick always hits as well, so there is no danger of retaliation, but you must take care to be far away enough from the enemy, or they will block the kicks and probably hit you after that.
Of the Double Dragon games I've played this one is among my favourites, and very deserving of a chance. I still have to 1cc Hard mode, and also play the GBA game.
Congrats on the 1CC.
It dovetails perfectly into the armlock mechanic, too. Also a nice source of potential drama if they duck your attack (SFC-exclusive mechanic), in which case you really will need to lock 'em up!
) scarred me for life. It's the only digital release I've been tempted to delete. 
For the love of god and all that is holy, stick to Psycho Soldier. 
Intriguingly big, bold take on sidescrolling run/gun, with UPL's customarily vivid style. Action is primordially simple yet tense dodge/shoot, befitting the big cartoony sprites - stages often consisting of one or two enemy types teeming across long flat expanses. Default character's shot kinda sucks, and he's a big target, but he can walk on air, among the most endearingly bent takes on doublejumping I can recall.
) are the busted camera tracking when hyper-hopping forward (you'll soon hit the screen edge), and the weapon switch on pickup. Grenades should've been on the D button, absolute deathtrap if you're switched to them with enemies nearby.
I had no idea the arcade version of Taito's Front Line uses rotary controls! A dial, rather than a twisting stick ala SNK, but regardless, this seems like the Ikari Zero that TANK most definitely isn't. The boned camera tracking makes my teeth hurt, as always, but the relatively low game speed seems to offset it. God damn, scrolling camera tracking is a cruelly underrated discipline.
) post explode into existence unannounced. 
Special thanks to dojo_b for proposing the idea, __SKYe for creating the index's first iteration, and all other contributors!