First and foremost, I want to preface that I was not expecting BioWare/CDPR-level romance, six scenes, etc. I would never expect BGS to do anything that extensive because they have no history or precedent for it.
However, what I was expecting was something with a bit more substance than Skyrim. In truth, the romance system in Fallout 4 is just the Skyrim system with a few tweaks. Instead of just having the option to marry an NPC immediately with the necklace of Mara, you have to build affection, similar to a BGS game.
Once your reach the maximum threshold, which doesn't take long at all depending, the romance is essentially complete, much like getting married in Skyrim. The benefits of your new found romance? You get a 5% extra boost for being well-rested if you sleep near your "lover" and you also get a companion-specific perk based on who you romanced.
I think what largely bothers me is it's not even really a romance. There are a lot of innuendos and suggestions that you are in a romance, but never once were the words "I love you" or anything nearly that explicit were made. I think even those words were used in Skyrim, even if it was a bit silly given how romance worked in that game. It's more so a "friend with benefits" dynamic in Fallout 4, and yet again I feel the "romance system" is largely pointless and over-sold by BGS.
What's actually ironic is you can have a one night stand with Magnolia, which will fade to black and take you to a hotel room the next morning. That is far more explicit and direct than at least the romance with Piper, which I just find to be a bit strange and peculiar as you aren't even really aware the romance has been complete as all you have is dialogue and then the achievement unlocks.
Overall, I think companions in Fallout 4 are better than BGS has ever made them before. Most of the ones I have come across are interesting and I could adventure with any of them, unlike the dozens in Skyrim who were all cookie cutter. The problem is there is really little reason or purpose to engage a "romance" as it has little value in the game from a character progression/storytelling perspective.