Would an Earth analog exoplanet which rotates around a solar analog, but without axial tilt, have no seasons?
Would it be similar to how Los Angeles does not have very noticeable seasons compared to other parts of the Earth?
There are several factors that cause seasons. In approximate order from least to most speculative:
If you mean a true Earth-like analogue (in the sense of being exactly-like-Earth-in-every-way-except-the-axial-tilt), then no--it would not have noticeable seasons, since none of the above factors really apply.
Exactly. Seasons and its difference between northern and southern hemisphere are caused due to the tilt of the Earth's axis. But this is not the only thing involved. An other important fact is the orbit's eccentricity: a very eccentric orbit would cause a whole planet "summer" when around the perihelion and a whole planet "winter" near the aphelion.
There would be also extreme permanent hot zones near the equator and extreme permanent cold zones at poles.
If it would not have any axial tilt, and it rotates in an orbit thats not really eccentric, it would have no seasons. If it has (really) high eccentricity, it would have seasons, but they would be hot all over the planet a part of the year, and than cold all over the planet the other part of the year. On earth, due to the axial tilt, we have winter in the northern hemisphere, at the moment that there is summer in the southern hemisphere.
I considered this as an explanation for George R. R. Martin's books, where several years could go by during each season. If the planet had no axial tilt and very little eccentricity in its orbit, there would be no annual seasons. But if solar energy output would vary sufficiently, you could have seasons, with inconsistent cycle times that measured in decades.
So I thought, "Ha, it is possible."
Then some character in the book noticed "the days were getting shorter" and I had to throw it out. In such a world, day length would always be the same, and it would always match night length.