Woodsmoke bothers my allergies so I love love love my heatandglo, with the campfire logs. We do NOT have electronic ignition; A) because we went with the cheapest options for all and B) because the installer dude told us that in the case of an electrical outage, our fireplace would keep us toasty. We just light the pilot light in the fall and turn it off in the spring.
Even if you have a pilot light, there is some sort of igniter system that controls the valve that controls the gas flow. The heat generated by the pilot/flames provides the electricity needed to operate it. This link explains how it works:
http://www.mygasfireplacerepair.com/how-gas-fireplaces-work/
A fireplace equipped with such pilot light/wall switch/millivolt igniter will work when the power goes out (this is what we have, and I am glad the builder installed these vs. fancier pilotless systems).
Our home is older and had a double parlor, originally with fireplace between the rooms (double sided, we believe.) The last owners took it out, made one large room. We considered replacing it, in the original mid-room. spot. One issue we had is that the remaining portion of chimney (3rd fl) isn’t wide enough to accommodate the standard liner (at the time; maybe this has changed.) You can place a direct vent pretty much anyplace and they run the piping. In some cases, the outside piping has to extend up above the roofline. In my area, at the time, there was some issue with using one of those big bowl shaped direct vents that just sit on the outside wall, with no stack.
In older homes in Europe, they often retrofit some gas replacement into an original fireplace-and it looks fine. Get someone in to analyze your situation, they’ll advise. Btw, when you’re adding a unit where one didn’t exist, it’s good to talk to your insurer. A cast iron would have increased our rates.
We have a masonry fireplace which is not on an exterior wall. We had it fitted with gas logs and remote control feature which does not require electricity to work. It puts out a lot of heat. I don’t know what brand it is, though.
So glad my H and contractor convinced me to install a gas fireplace instead of a wood burning in an addition we added 13 years ago. While I love a woodburning fireplace, they reminded me of all the work and dirt. Since I had been there and done that with a wood burning fireplace ( since birth actually, although didn’t do the work as a kid, ha), I went along with the gas one. It is also a source of heat in the addition.
Well we have a fire every night in the cold season. It is comfy and emits warmth and glow. It doesn’t crackle. But it also doesn’t have ash and wood chips. I love it. We would never have a fire every night if it was wood burning. And I am now too darn old to be, stacking and lugging in fire wood, cleaning ashes, etc.
Converted two woodburners to gas. Love it. Instant on, instant off. No maintenance. No ash. No cleanup. No worries about cresote and chimney fires. Clean enough to use even during a no-wood-burning-air-stagnation advisory. We didn’t use artificial logs, opting for glass chips instead, which is very contemporary in appearance. (The only catch is no ashes to throw on icy sidewalks.)
My last house was a fairly pristine post and beam structure built circa 1790. It had the classic massive central chimney, with fireplaces off of it in two rooms. The main fireplace was really big, with the original pot crane and a beehive oven with what appeared to be the original wooden door. (If not original, it was definitely early19th century, at least.) I loved sitting in a rocking chair by that fireplace, and it would have been vandalism to convert it to gas.
Our current fireplace is much smaller and surrounded by Victorian-style pillars and moldings and so forth. (All of which have, unfortunately, been painted white. 
I wish they were still oak. ) It really is not suited to a crackling wood fire, physically OR aesthetically, nor would a woodstove in the hearth work. I’ve actually wondered if it wasn’t built for coal, although it isn’t a shallow as some coal fires I’ve seen. In addition, my sinuses act up when I’m subjected to wood smoke, and who knows how well the chimney would draw…
I want something simple that won’t take away from the woodwork. But we definitely won’t be going for anything modern looking! 
Thanks to all for the great info.