I don't play a lot of tactical games; it's just not my jam. Occasionally someone will ask me to explain why it's not my jam, and there are several reasons, sure. Even the simplest tactical games are still a little too complex for my taste. I'm also not a big fan of turns that take twenty minutes to play but represent five minutes on the ground. And then there's a tendency for the hexes to get overly congested: I have a stacking limit of two units per hex, but one or both of those units can be a vehicle which can in turn transport two more units, and each hex can have a leader, so now we're up to, what?, seven counters?, only these units have moved (so we need move markers) and these units are pinned (so we need suppression markers) and did I mention that each of those two units in each of those two vehicles each carried a special weapon? No and thank and you, man.
But really, the thing that bugs me most of all is Op Fire. I understand the purpose, even the necessity, of Op Fire in a tactical level game. And I don't have a problem with the fact that you get to make decisions on my turn, because that kind of interactive back-and-forth can be very exciting. But I don't particularly like how it's implemented, which usually looks something like this. "Okay, I'm moving these dudes. They have 5 MP. I'm moving them into the first hex, spending 1 MP - do you want to Op Fire? No? Okay, moving them into the second hex, that's 2 MP - do you want to Op Fire? No? Okay, third hex, it's rough terrain that costs 2 MP, so now we're up to 4 MP - do you want to Op Fire?"
Obviously in practice it isn't quite so verbal, but for me the slight pause before moving from one hex to another is cumbersome. And then when we resolve the Op Fire, I have to remember how many MP I had left - wait, did I start in this hex or that one? More than that, I find the decision of when to Op Fire and when not to, and which hex to Op Fire into just a little too much to chew on for this bear of little brain.
Again, it's not about the concept itself, but all about the implementation. It doesn't bug me in a game like Combat Commander - just about the only tactical game I can really get my head around on a regular basis - because the ability to Op Fire is contingent on having the right card in your hand, and you play the card as an interruption to the normal flow of play. It happens sparingly; it's not something you need to check on every hex of every turn.
Some games, usually pre-WW2 games, handle this through a Defensive Fire Phase that takes place between the enemy Movement and Combat Phases, and that can work well enough, but often doesn't simulate the feeling of moving within the enemy's field of fire. The problem of course is that one side can push their troops right to the edge of the enemy's range on one turn, and then close the gap on the next. I remember reading an article by the late Wally Simon about this problem, and his solution was simply to double the historical range of the firing units. Now the defender would get in at least two shots before the charging units could close the distance. Being that I once caught flak for having a rifle range that was one hex too far, that's not a solution that I would want to recommend, but I can appreciate its elegance and simplicity if not its historicity.
I haven't had to tackle this problem all that often myself, though there was a spell where I was working on a World War I game and needed to simulate the difficulty of moving in No Man's Land. That game, which was to be on Fuller's Plan 1919, didn't come to fruition - I couldn't wrap my head around a lot of the other aspects, and it was intended to switch between large operational-scale movements and small-scale tactical battles, and so was perhaps overly ambitious. Eventually Mary and I asked John Gorkowski to do a game on the same subject, and I still think his Plan 1919 is unjustly overlooked. But I'm digressing.
The one thing I did get to work from my abortive design was my approach to the Op Fire/moving against opposition problem, which was to establish "Approach Zones" emanating from the enemy line. Entry into the first Approach Zone hex was free, but each additional hex entered during a single move phase would cause a disruption of the unit or, if already disrupted, a step loss. This mandated a slower approach, and during the enemy turn they would of course be able to fire normally, compounding your losses. I thought this solution of "automatic, mussless, and fussless Op Fire" to be rather clever, and I lifted it, with a few adjustments, to serve as the core of my Agincourt game, We Happy Few.
For many, of course, plain ol' Op Fire as seen in a million tactical games works just fine, and if it ain't broken, why spend your time and energy trying to fix it? But just because everyone has done something a certain way, doesn't mean it's the only way of course, and it may be worth it for designers far cleverer than I am to approach the concept anew, from first principles.