Despite my MacBookPro spec far exceeding the game's minimum requirements, the game juddered to a virtual halt after an in-game Save & Reload.
Contacting Aspyr's Help-Desk, they asked for a System Report, and four hours (!) later they provided the solution.
THIS APPLIES TO ALL RECENT Hi-Spec MacBookPros and others having both on-chip AND discrete graphics cards.
Go into your system preferences>energy saver> and turn OFF the option for automatic graphic switching. This will enable only the Nvidia GTX 750 and not the Intel Iris Pro. Once you have turned off automatic graphic switching, relaunch the game.
[If anyone else decides the OSX/Download route, be aware Steam downloads both PC & Mac versions onto your computer. Unhelpfully, they don't clearly label the folders as Windows/Mac, and attempting to open the wrong one first generates an unhelpful error message.]
On to the game - the internet is awash with praise for Civ IV BTS. It's all true.
Civ IV is still the all time great of Strategy Games. Built at a time when there was more focus on Game features, and less on forward Corporate Cash Flow, Civ IV remains the pinnacle of Strategy Games. Its interface was built at a time when less power was available to Graphics and therefore less general options and abilities available to the developer. Its interface is a little dated now by todays common practices; but non the less its highly acceptable, and STILL remains the "Strategy Game to Beat" in the Games Industry - the all important Game Play is Outstanding.
As with all Mainstream Games it attracted the usual Premium price on initial release a few years back. Now some years have past, all the Version releases are available at Bucket Shop prices. If you are one of the few on The Planet who have never played Civilization Series before, go get this Complete edition, its a steal at this price - it represents Games that cost £Hundreds in total when they were first released. The game is as good as ever, the cheap price is because the mainstream Community already have it, if you don't, then run to buy it. A new Player to the Civ Series will download (literally) months, if not a couple of years of evolving game play before you put down the mouse with a WOW feeling.
The great Strength of the Civilisation Series has traditionally been the incredible game play, where you could use your brain, not get satisfaction from mere graphical whizbangs. They dropped the Ball with Civilisation V, and I suspect Sid is livid about it all (don't blame him, the guy cant be everywhere). With Civ V, the Corporate Money Men grabbed control and you can see their grubby fingerprints all over it. The second expansion of Civ V has retrieved the situation somewhat, but the damage to the reputation of an All Great Gaming Giant has been done. If you are new to the Civilization Series, get this compilation, accept a slightly outdated front end, and enjoy - give Civ V a miss. There is little doubt Sid is swinging his fist in the Background, and Civ V! will on release restore the Civilization Series reputation. Meanwhile grab this great value pack and enjoy for 2 or 3 years, until Sid gets Civ VI up, running and back to the Civilisation Series normal high standards that were slammed by the Civ V Dog of a game.
At this price, Civ IV is a no brainer - go for it.
It is not AT ALL clear enough from the sales listing on this product that the download is via Steam.
Steam have stopped supporting OSX Snow Leopard (which is listed on the product listing as compatible for this download) so therefore this download is NOT compatible with Snow Leopard either.
If it had been clearer on the product listing about the download being via Steam, then I would have known the game would be undownloadable because I had already done my research and knew that Steam doesn't maintain a Steam client for Snow Leopard anymore.
Steam's own listing for the product is £5 cheaper anyway!!!