Hi there,
I'm assuming you have the 5 speed box with the car being one of the last models, and I only have experience of the 4speed 352 box but I'll comment in the hope that the same things apply across the range. Gear changing isn't what you'd call a strong point with these cars, and if you're coming from a modern car then it's going to feel awful. That said, you do adjust with practice but I'm really saying that you might have to "manage your expectations"
Reverse detent; on mine there's not much that can be done, it's simply a case of assemble the spring & ball and that's it, no adjustment. I suppose you could fit a stronger spring, but there's nothing I can see otherwise. Having assembled it, if you try to twist at the gearbox selector shaft end then there's notable resistance, but by the time you have all the linkage in place with the weight of the tubes on it, I agree that at the gear lever end it feels like very little resistance and I think that's normal.
But it's not what I'd call "slop", which I'd interpret as the linkage moving but not the gearbox input selector shaft. The trouble is that we can get free play in too many points;
1. Gear lever bushes
2. 1st UJ by the exhaust downpipe
3. Rose joint (Heim joint ?) and supporting swivel bush
4. Final UJ at the selector input shaft end.
Sadly, you need all these areas to be tight to give you half a chance and the even sadder fact is that there's no adjustment other than replacing with new. Gear lever bushes probably make the most difference and are normally the first area for attention.
You can assess the UJs by twisting both shafts and feeling for movement, basically there shouldn't be any. A small amount is normal (a few thou') but you're aiming for none at all, just as in a driveshaft UJ. I believe you can still get replacement parts, or it's possible to overhaul your originals using donor parts from steering joints but you'll need a press or vice for that.
The last time I pulled mine apart I did the following;
1. Remove centre armrest pad, scratch your arm to pieces by undoing the nut holding the gearstick to first section of the tubular shaft. That drops the shaft into the tunnel.
2. uncouple the gearbox Uj
3. Uncouple the swivel bush from the engine/bellhousing
4. slide the complete linkage out of the car.
I think I once managed it by leaving the gearlever attached to the linkage but just releasing it from the chassis (4 bolts underneath the lever gaitor) but that's more of a hassle to angle the mounting plates through the centre tunnel. However you do it, it's not something that you'll want to do twice so my advice would be to make a careful assessment and replace anything that's even slightly worn.
Try this page for some more hints,
http://lotus-europa.com/manuals/index.htmif nothing else it'll show you that you're not alone with the problem
Brian