What an interesting topic!
I started out with vanilla Minecraft, like a lot of other people, and played it until I knew the drill pretty well. My first mod pack was a "Lite" one from one of those *other* launchers, back in the 1.4 days... and while it had a lot of problems, I had the time of my Minecraft life with it. Finite water was a real eye-opener, since water tends to be more of a minor annoyance in Minecraft than an actual resource. I didn't understand Buildcraft too well at the time and got frustrated with exploding pipes and engines. I started trying out different packs from different dev teams and eventually got into assembling my own packs, which I still enjoy doing.
Over time, I got into more and more "magic blocks" kind of mods, which were quite seductive for a while, but I soon found that teleporting all the ores out of the ground in the blink of an eye and rapidly smelting them up into three or four or five times the vanilla yield left me with a lot of stuff, often more than I'd get around to using for anything. Modded Minecraft just about always encroaches on creative mode eventually, unless one stays close to a vanilla feature set. I really do enjoy creative building, but I need a certain amount of "game" to keep me interested in doing that.
My current compromise is not what I'd consider "hard mode", rather I would term it "interesting mode". And what makes tech mods interesting for me is constraints. The pack I'm playing now is similar to what CJ uses in his Dark Tower series on Youtube, minus Twilight Forest and adding some things I can't live without, like Carpenter's Blocks, Chisel, JABBA, SC2, Tinkers' Construct, QuarryPlus and Logistics Pipes. For what I want out of mods at this point in my journey, I think I've just about hit the sweet spot. It's definitely not "hard mode"; I haven't changed any recipes or added GregTech. But the mods I'm not playing this time around are worth noting as well: namely, Thermal Expansion, EnderStorage, and anything involving spooky action at a distance, aside from Thaumcraft's Magic Mirror. My innate laziness tends to overcome my good intentions to build logistics infrastructure when I can just pipe some nether lava into some inexpensive dynamos and never have to think about power again.
What I really like about mods is bodging all the toys and gadgets together and seeing everything work. I like for the engineering problems to be in base design and logistics more than in resource-getting, which almost every mod can do now using brute-force methods anyway. For example, what I used to find annoying about BC pipes seems interesting to me now that I have absorbed a bit more knowledge. Engines that need fuel, water, and engineered control systems in order not to explode not only makes a certain kind of sense, but it provides an interesting challenge to operating a base that I can't really get from plopping down a compact solar and filling up what amounts to a big battery. LP seems to fit the feel of Minecraft better to me than Applied Energistics does, and I like how it's easy to build an LP system on top of the same chests and barrels I make when starting out in a world, not to mention the absence of idle power usage.
No doubt it may seem strange to some, as it does somewhat even to me, that as the mod world speeds towards Redstone Flux I'm now playing a pack that only has Buildcraft power. I understand why RF has become the dominant paradigm, but I do hope that the MJ-based mods will continue to behave in the same way they do now even though they may change to use the RF API internally, as Buildcraft is already beginning to do. The MJ API might be old fashioned, but the play style of the classic mods really is fun and just more "Minecrafty" in my estimation. Perhaps I missed my true calling as a railroad modeler?
Or maybe I'm just a sentimental old fool.
Pace is as important to me in games as it is in fiction. That seems to be true for others as well to a greater or lesser degree, and it's just a great thing that there exists such a variety of mods and mod packs. It has become one of my major considerations when putting a pack together. I find more and more that I prefer the pace of the MJ mods. Clearly, most folks don't these days, and so it is just great that everyone can find something to suit their ideas of fun.
