FINALLY read this... I love Sir Pleamo's buildings
Everyone probably knows I LOVE assembly system (ok, you call it Steck..), and mostly hate System X. Except for the dark invaders

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At the time we bought ALL the sets, our first reaction to that first System X castle was to go to ebay and buy a few assembly castles.
However, I find myself changing my opinion on System X, mostly thanks to Sir Pleamo.
System X has, IMO, 4 + 1 major problems.
First, the holes. Both me and my sister find them ugly and unnatural (an opinion NOT shared by all the docs in our playkingdoms, who see they'll never be out of a job!). They make the buildings look unfinished.
The second problem is the cheap look the thing has. The System X castle looks (and feels) like a cheap plastic toy. Not playmobil. However, that is probably a matter of color, and quite easily fixed.
The third is a matter of design - most sets have half a house. No roof, no walls... makes it look kinda stupid. But if we had the parts available, it could also be fixed.
Finally, there's the JOY of putting HUNDREDS of those stupid little things in the holes. It is NOT fun, it's time consuming and boring. A side effect of this is when taking the building down to put it away, those stupid little pieces have a mind of their own, regarding on which "wall" (or whatever) they remain with, making it harder to box everything. This I see no way around. BUT... it does allow a versatility not found anywhere near assembly system. So, it can easily be seen as a trade off. After all, on the other side of this we have those clip ons. And NOBODY wants that, right?
The +1 problem is this...
what I want to say is, I have realized that nearly all categories that w know from Steck are no longer true in SysX! There is no top side, no bottom, no left no right... there are only size, number of conecting holes and colour, the rest is imagination!
But that is MY problem, and not the system's, me thinks. AGES ago, I discussed the System X vs Assembly System, and Richard told me (and I agreed!) the major point I saw for system X (how versatile it is) was really not an advantage, since we can't make head or tails of it!
Now I think that WE need to adjust our perception of it... May not be easy... but if this old dog can learn that new trick... who knows..
I guess Sir Pleamo is correct in thinking we're not gonna get Assembly back. And it's stupid to have a bunch of incompatible systems anyways. And those clip ons are ridiculous. They really don't seem to like money. By making it impossible to expand those awesome looking tower/castle, they limit their own sales... is that reasonable?!
So I think our best bet is indeed to turn to System X (AGH). With different colors and new parts, it could probably be a great system. Ok, we'd still have to put hundreds of little pieces in place. We'd still have to adjust our thinking to be able to actually build anything with it, but after we did, the possibilities are virtually endless, something that is not true with Assembly.
IMO, the holes need fixing though. I don't know how, but (at least for me) it is a must to make acceptable buildings.