I have pointed out before that you can use JA2 1.13 to play Unifinished Business and WildFire, though not in their vanilla state. Currently the same holds true for JA1, since the team behind Night Ops is working on taking Metavira to the JA2 engine.
As to whether JA1 and JA:DG are worth it, it depends on whether you can work with their interface once you've played JA2.

While the graphics of JA2 are far superior to the ones of JA1 I would say that JA1 is definetly worth it.
Actually when JA2 was released it was a disappointment for me at first, because I was missing some stuff from JA1.

JA1 has enemies in all sectors, which makes it a longer fight for victory. It also has a different and imho better ressource management system. You need to decide where to put up guards, where to put harvesting guys and so on. After each day you get somewhat of a recap of what happened this day, which always feels awesome.
There are also sectors where you get special advantages when you sneak. There might be a hidden stache which explodes once the enemies spotted you - no such thing in JA2.
You also have microphones within the game where you can listen to the talking of your enemies. Never had any advantage from that, but it was fun anyways.

In addition it's also fun to get some of the backstory. While the games have no "direct" story which follows up, they have a timeline and all of the mercs have their background story which was worked at in each game.

Maybe you remember lynx and buzz. In the first part Lynx is solo, in DG he has a relationship with Buzz and in JA2 they hate each other. And that goes for tons of characters, like Larry with his drug problems and so on. In JA2 you have got a whole hall of fame of old characters. Ever wondered who these guys really were?

JA1 also had native characters, like you have Dimitri in JA2. Remember Hamous from JA2? Well, he appeared as native in JA1, and became a Merc in JA DG.

If you love the story and the backgrounds of JA, you should check out Jagged Alliance 1. It also has great gameplay of course.
JA DG however is mostly aimed for multiplayer and I would not necessarily recommend it if you only play it singleplayer.

What a great post, Kordanor. Perfectly summed up! JA1 is still to this day one of my favourite games. I even have a hand-made excel spreadsheet that shows all mercs and their stats from JA1 and how their stats change in JA2. I play the games like a continued story so the hall of fame in JA2 is just such WONDERFUL fan service to people like me.

JA1 is definitely worth playing if you can get past the dated visuals (heck even JA2 is "dated". To me, the visuals in JA1 are art. Same as JA2), and the lack of a more user-friendly interface. Things that were perfectly common at the time.

Thanks for all the answers guys. I really appreciate it.

I think I will get the JA1 titles at a later date. My TBS plate is kinda full these days.

Thanks again for the answers.

If you start with JA2 then you will have a hard time getting into JA or JA:DG . JA2 is just plain far superior in every way. I realize we all have our nostalgic feelings and we all prefer the games we are most comfortable with, as opposed to games we have to spend many hours learning the ins and outs of but having said that JA2 will be easier for a new person (to the JA games) to get into because of the interface improvements and graphics and such. JA and JA:DG are great games, don't get me wrong. But JA 2 just benefited from being a few years more 'modern' in it's development. It is a great RPG with heavy tactical features whereas the first JA is a great tactical game with some RPG elements.

Thanks. You have made some good points. I think I will stick with JA2.