Since it doesn't have any reviews yet, let me briefly summarize the whole series here in one place.

A Love Story is a predominantly city-mission series (except for parts 5.1, 5.2), the premise of which is doing a number of tasks to help your buddies in their love affairs. Fetching items constitutes the bulk of gameplay in the series, with an occasional escape/rescue scenario. The lists of items to procure tend to be lengthy, even outside expert difficulty, and often seem a bit forced. The challenges will sometimes feel really unfair with some ridiculous key item placement, or vital items appearing out of nowhere without notice in the weirdest of places, but most of the time it's about fine, just pay attention to the guards' slightly hightened senses.

The worldbuilding in the series is a nice study of progress. Missions 1 and 2 look especially plain in terms of spaces and architecture, then you can see a lot of improvement in parts 3 and 4, while the two final missions already display the hand of an accomplished creator. Beggining with part 3, most areas show original, distinctive character.
Part 3 is set in a shopping district with lots of stores and inns to visit, but I felt it was too ambitious in its scope, with some new mechanics not working well, too many uninteresting, RPG-like fetch quests, and unpredictable AI behavior. The choice of color palette is also startling, presumably made in attempt to imitate sunset, but ending up looking rather surreal and slightly off-putting.
Part 4 features some quite moody and original slum district, in my opinion the most atmospheric chunk in the series, ending however in a peculiar rescue quest.
Parts 5.1 and 5.2 depart from the city setting of the series and focus instead on a mansion/fort-like complex and an abandoned Hammer cathedral. In 5.1 gameplay remains quite the same - you get yet another list of items to procure, but due to reduced scope and playing area it feels much more pleasant. There are also multiple interesting hidden challenges to be discovered and completed, while the visual design, brushwork, and texturing are already on a high level.
The final mission in the series is probably also the best one. It is very impressive on a visual level, quite atmospheric and features a couple unique mechanics you won't find in any other FM. It makes you notice and appreciate little, unexpected things, like a guard dropping an oil lamp and it getting aflame. Unfortunately, most of your challenges will again include loads of running around and looking for miniscule items hidden in a big place. At least there are once more many additional, optional tasks and secrets to be uncovered. You also get a satisfying cinematic resolution to the series.

There are some interesting city sections in the whole series, built differently than in most FMs. You may want to check them out, if you don't mind unconvincing or just plain cheesy storytelling and several baffling objectives. If you're only into highest-quality designs, though, you might be better off just going for parts 5.1 5.2, which won't make sense storywise, but then again, the story isn't great anyway :) In any case, the last two missions are really good and deserve much more credit than they get.