Got back in late August from the 2 weeks in Algeria:

Algiers 5 days total, did a day trip to Tipasa and a city tour of Algiers.

Constantine for 3 nights, stayed in the amazing Marriott hotel and did day trips to Tiddis, a deserted small Roman Ruins about 20-30 min from the city, and then also a trip to the magical Djemila, a 90-minute trip from the city. A stunning, huge, also-deserted Roman Ruin.
We did not have a chance to get to Timgad, which I'm told is just as big as Djemila.

Sahara Desert 4-day, 3-night trip. Flew to Bechar, then had a local guide for just about the whole time. Stayed at the very comfortable Hotel Saoura Taghit. Did a day trip to Beni Abbes and went swimming in the local spring water pool, did camel riding, dune climb, camel herder visit, walked around the town, sat by the hotel pool. This was in August: 115 degrees F every day, but actually tolerable and absolutely zero, zero foreign tourists in the entrie 4 days.
Kidnappings? Well, if you're working for a petroleum company in the desert, then 4 years ago you might have had a problem. But that was the only incident in the last 4 years. I couldn't guarantee your safety, but I can say that I felt absolutely safe the entire time we were there.
When driving between desert cities, you have to register with the local police office in both your departure and destination towns, so the police know you made it ok. Even Algerians have to do that. However, one interesting thing is that foreigners travelling between desert cities also get a (free) military police escort SUV trailing your car. It was weird at first but actually the guys were nice and said that (at least in Taghit area) nothing had happened for 20 years.
So, it's up to you but at least for me, I've already got plans to return and see more. There are NO TOURISTS AT ALL-- in our 13 days doing almost exclusively touristy things, we met TWO tourists-- a British woman and her son-- and otherwise we were treated very well and as special guests.