I've got a 1.5.2 mod pack you can download via the Private button on the launcher you can use to get your feet wet with some of the new changes. The code is 'ShneekeyCraft' (caps are important, but not the quotes).
Thermal Expansion does a lot better job of ore processing than IC2, and is a lot more internally automated... you can set a Pulverizer directly adjacent to a Powered Furnace and configure them so that you don't need pipes or tubes or transposers or any of that nonsense, they just hand it off to each other seamlessly. It also introduces Redstone Energy Conduits and Redstone Energy Cubes, giving you the ability to store Buildcraft MJ. It also has Tesseracts which are basically Teleport Pipes done properly. The energy tesseracts do carry a fairly stiff energy loss (20% in the latest version, 25% when it came out, configurable in the .cfg file).
Forestry is included, but tbh, it isn't nearly as good as you remember. All of the different farm types are gone, replaced with a very expensive multiblock. Fertilizer is now only made with Apatite, and while one vein of Apatite can last you for months, it's still a finite resource. However, the backpacks are worth the mod by themselves, and there's a LOT of work that has been done on bee breeding, and now includes tree breeding and even butterflies.
Minefactory Reloaded is an old mod which has been revived by the original mod author. Quite frankly, it's my go-to for automating farms, since it can also automate animals and their resources. It also includes Rednet, which puts even RP2's red wire to shame. It is a very inter-connected mod. The output from one setup can be used to fuel/boost another setup somewhere else.
Anything you remember about Equivalent Exchange 2 is probably best forgotten when playing with EE3. He's gotten rid of a lot of the crap, and it is still very much a work in progress. So far, he's got a Minium Stone, but the ability to transmute is still limited. Sorry, no RM blocks by the second hour due to darkrooms or cows anymore.
There's a new pair of mods, Tinker's Constructs and Natura, which add a lot of really nice options for you. The former includes tools that are actually worth using, and can be obtained fairly early on. It also has an upgrade system which puts Enchanting to shame. Natura adds a bunch of worldgen for you to explore and exploit. Tinkers Construct has in-game documentation for you to read up on, which is pretty amazing.
Railcraft now has Steam technology. A Boiler generates steam, which can then be piped to steam engines (MJ) or Turbines (Eu) to generate power. You can generate quite a bit of power this way, but they tend to be fuel hogs until they get warmed up, then they become the most fuel efficient in the game.
Modular Powersuits is a very innovative little mod which delivers powered armor and tools. Eventually, they can outstrip parts of Quantum, although there are some trade-offs in functionality, and the tool can replace both the chainsaw and the drill and the mining laser, with enough upgrades. It won't be cheap, of course, but it can pretty much suffice for all your mid to late game gear requirements.
In 1.4.x, Redpower 2 has Computers which run off of FORTH. If you don't have much programming know-how, it can be difficult to get them going. If you do, it is super-crazy-awesome.
While I don't have it in my mod pack, ComputerCraft has been a big star lately. Personally, I consider it way too easy. The computers are coded in LUA, which is simple enough that even my eight year old can look at the code and tell what it is doing. Turtles are... well... anything you can do, a Turtle can do automatically. Anything. Oh, and you can Pastebin code and share with others. So even if you don't know how to write code, you can just use someone else's.
IC2 is... well, there's a change to the nuclear reactors. A very huge change. CASUC's are dead, but you really don't need them anymore. The successor, the CRCS, can also net you thousands of EU/t at fairly high efficiency, but require a BUNCH of secondary 'cooling tower' reactors. I also came up with a Tower of Power build, similar to the old watermill towers, which can produce 7k+ EU/t in a Mk. I configuration. I don't have this in my mod pack either.
GregTech... is a push-button topic. Most people either really like it, or really dislike it, and there's almost no middle ground. It changes other mods recipes (or at least other mods have config options which get enabled when it detects GregTech) to make them a lot more complicated. Not more expensive, generally, just more complicated (although the macerator recipe that calls for diamonds, plural, will probably tick you off). For this reason, opponents of the mod call it 'GregNerf' or something like that. I wouldn't necessarily call it a nerf, but it does require a lot more infrastructure, and it requires that you baby your infrastructure, to keep it running smoothly. Recently, he did something rather controversial that pissed a lot of people off. Enough that the thread discussing it got locked by a moderator. So there's at least more animosity than usual aimed at this mod right now.
Applied Energistics. Do you remember Logistics Pipes? Well, Krapht hasn't had a chance to make a new version since 1.2.5 (although someone is updating and maintaining a fork of it), and this mod sprung up to take the place. It isn't cheap to get into, it requires constant power, but it has monumental storage capacity which is automatically sorted, auto-crafting, automated tasks, crafting with other machines, and in general fills the same niche that logistics Pipes did. It is primarily good as a large extended network, but not so much for smaller systems. Generally, one uses another method of item transportation (pipes or the MFR conveyor belts) to bring items from remote locations to a central hub to be picked up by the Applied Energistics network.
