A few months ago I purchased the Complete Naval Combat Pack directly on Strategy First's website as a digital download. It consisted of the games 688(i) Hunter/Killer, Fleet Command, Sub Command & Dangerous Waters. Out of these four games, two (688(i) and Fleet Command) work out of the (digital) box. Sub Comoumand and Dangerous Waters have a broken activation system in place that won't let me run the game. It acts for a CD key (which none had, and there were no DRM keys indicated in the order e-mail). I e-mailed Strategy First's support department regarding Dangerous Waters and didn't get a response (a patch for Dangerous Waters) until I sent a followup e-mail. That was at the end of February
April 9th, I decide to fire up Sub Command. It has the same exact DRM, same exact problem. Sent an e-mail to support. I expected at most to be kept on the hook for a week, maybe two at most.
In three days, it'll be a month to the day I e-mailed them for a patch. No response at all. I just sent them another e-mail and I'm pissed. I paid close to $50 for that pack. $50.00, which translates to a truckload of GOGs or Modern Warfare 2. $50 for games that range from 7 to 15 years in age and only two work.
This is a case in point that DRM is getting out of hand. I'm a paying customer, so I expect my money's worth in product AND in support. I could've probably pirated these games, but instead I wanted to show support for the developers and forked out green.
Nice job Strategy First. You just lost any further possibility of sales to me.

I thought that it was rumored Strategy First doesn't pay its developers.

^ - RTF(ine)P, I paid for this back in February.

Strategy First have a long history of dodginess. It would have been better that they just went under completely.

I bought all the games from retail in the past. I don't remember any form of online activation, apart from Dangerous Waters which I didn't buy.
Anyway, I would suggest you to buy the complete naval pack at a much lower price from Steam as I did last year because I couldn't find the discs. I bought all of them for like 10 or something.
At least get it if you get your money back from them.

Would it be unreasonable for me to threaten them with legal action? They haven't answered my follow-up e-mail.

It's not unreasonable. But it would mean joining the back of a long queue. You're far, far from being the only one that Strategy First owes. They seem to stay afloat through the simple virtue of being a turd.
What I find works better is the threat of bad publicity. If you give them an ultimatum of 'give me my money back or I'll spend some time writing to every relevant publication I can think of' then you should hopefully see something more along the lines of a productive response from them. Although, given that they're already so far down the crapper even that might not work.

Don't bother with that unless you're actually prepared to follow through on your threat. The easiest thing to do is request a refund, and if refused then contest the charges with your credit card company (assuming you paid with a credit card). If you really want to pursue the issue through the courts then you could take them to small claims court, although this would involved a bit of a time investment on your part. In the final analysis, though, unless you're ready to invest time to simply pursue the thing on principle then unless you can issue a chargeback the best course is to just take it as a learning experience and avoid dealing with Strategy First in the future (and also research your purchases a bit more before buying).

That's the perfect case for a chargeback. Look up who to call and set one up with your card and initiate a chargeback. They suggest you contact and settle the issue with the people you bought services from but a law was made to protect customers from poor service with chargebacks. Now of course you do this to Steam they will lock your account but it's apparent you won't be buying from Strategy First's website again so it won't hurt and you will get your money back within a month usually after filing the chargeback.
Snap didn't read end of that one, got ninja'd without knowing.

Well after today's e-mail, SF finally decided to get up and give me a key to activate Sub Command with. Still ain't going to shop with them anymore