So are you guys bored with this game yet, or does it truly provide years of playability?
I have 157 hours, one playthrough of the main storyline and I am ~ Level 62.
So far, I still like it and I play it almost daily. I like the range of activities that are readily accessible. If I want so action, I can investigate a POI or take a bounty contract. If I feel like doing some misisons, there are plenty of quests and mini storylines available (just like in any other Bethesda game). I can be creative and build and decorate my outposts or housing options or just go exploring. Starfield has indeed become my Elite replacement.
Some storylines are great and others are "only" okay. So far I haven't met a single storyline where I would say "meh, that was bad". Even the main storyline is okay. It's a good twist on the whole "repeated playthroughs" topic with some surprises in the plot, some really great moments and some missed opportunities along the way. As I said, it's okay. Not great, but not bad either.
The economy feels "alright". The 5000 credits limit of vendors is a bit annoying, because it's not stopping me from selling all my loot. It just means I have to spent more time running around to sell my loot. Building a decent (endgame) ship from scratch costs ~ 350.000 to 400.000 Credits, which is about right. Not too long, but not to easily obtainable either. The "bottleneck" that will take the longest time is probably leveling the skill points for better modules.
I'm not going to lie, there are a few things that irk me (but are obviously not bad enough to make me stop playing the game):
After 150 hours, the POIs (especially for bounty hunting missions) can become repetitive.
Bethesda missed the opportunity to introduce a basic command menu for your companions (go there, advance, fall back, use X weapon, attack target etc.).
I still haven't figured out if it's a bug or a feature: The game throws low level and roughly equal level opponents at me at the same time. There can be a level 5 dude that dies to a single bullet and right next to him is a level 45 guy that feels somewhat more appropriate. Same applies to ships: Sometimes I run into Level 5 ships that escort level 38 ships.
While there are plenty of weapons, there could have been more. But you can always have more weapons, can't you?
I've run into a few bugs, that have been annoying, but nothing game breaking (like a bunch of resuced scientists that refused to leave my ship after completing the mission).
To conclude: For a vanilla Bethesda game without mods, Starfield is already a fun game that can easily provide hundreds of hours gameplay. For comparison: I have played multiple different characters in Skyrim and I liked that game a lot, but "only" got to 455 hours in standard edition with an additional 39 hours in the Special editon. Fallout 4 (another great game) comes at 378 hours in multiple characters and Fallout 76 with 185 hours on steam (with pre-steam Fallozut 76 I should be at ~300 hours again). What am I trying to say here? In all those games I needed multiple years to get to those hours played and all games were heavily modded. In Starfield I got to 157 hours in about a month and haven't even installed a single mod yet.