Plans for the last big chunk of open land in the heart of the Seaport could be locked in on Thursday night. But as is often the case with anything involving building in Boston’s newest neighborhood, lots of people still feel something is lacking.

After months of debate, WS Development’s plans for 10 unbuilt blocks of the Seaport is scheduled for a vote at the Boston Planning & Development Agency. In exchange for the right to build 1.3 million square feet of extra housing, retail, and office space in the booming district — beyond the 6 million square feet approved seven years ago — the firm has added theaters to the project, revised its open space plan, and committed to keeping popular District Hall in place through 2033. It sweetened the pot further on Wednesday, promising a $7.5 million endowment to run the theaters and $3 million to go toward rebuilding the Northern Avenue Bridge and maintaining Martin’s Park along Fort Point Channel.

Despite all that, critics believe the Seaport — still lacking a library, school, or large park — may never become a bonafide neighborhood.

“This is like the last best hope for creating a heart and soul for the Seaport,’’ said Kathy Abbott, president of Boston Harbor Now, which advocates for public space along the waterfront. “How this space is developed and how it is programmed will matter a lot.’’

The back-and-forth over public benefits from Seaport Square — hashed out through months of public meetings, and many private ones — reflects the sometimes-transactional nature of big development in Boston.

Theater groups mobilized after WS dropped plans for a 200,000-square-foot performing arts center that had been approved in 2010. The developer eventually added two smaller venues to its plans and then an endowment to pay for their operation. When backers of District Hall voiced concern about the future of the civic hub – which originally was planned to be temporary – WS agreed to extend its lease. And the developer said it has committed to making $25 million in improvements to streets and public transportation in the area.

“Seaport Square is an extraordinary project that will transform the entire South Boston Waterfront,’’ said WS senior vice president Yanni Tsipis. “With this great opportunity comes a responsibility to make major investments in the performing arts, public infrastructure, and parks.’’

Not everybody wound up happy. The Boston Lyric Opera, homeless after leaving the Shubert Theater last year, didn’t get the larger theater it wanted included in the project. Supporters of a library in the Seaport have thus far come away empty-handed. Talk about plans for a school, envisioned a decade ago by the site’s previous developer, hardly even came up this time around.

Ultimately, the Seaport will need community spaces — open to all, free of charge —if it’s ever going to feel like a genuine neighborhood for everyday Bostonians, said State Representative Nick Collins, who has pushed for a library in the plan.

“Our public spaces are what make a community,’’ said Collins. “Our schools, our libraries, our parks.’’

WS says it’s committed to creating a Seaport that’s a welcoming place. It expanded park space and added playgrounds to its plan and pledged to build the required affordable housing — more than 250 apartments — on-site, instead of financing it elsewhere in South Boston as some developers of luxury Seaport projects have done.

The firm says it also hosts free arts and fitness events in the Seaport’s parks. It also points to the range of retailers moving into existing storefronts nearby — many of which WS, a veteran retail developer, manages — as evidence the area is becoming less like a construction site.

Some residents agree. Among the dozens of public comment letters received by the Boston planning agency were a number from neighbors praising WS’s efforts so far and looking forward to more of the same in the new buildings.

“In a relatively short time, this once-desolate area has become so vibrant and exciting,’’ wrote Fort Point resident Amy Donovan.

“The Seaport is finally starting to feel like a neighborhood,’’ wrote Kaitlynn Moore of South Boston.

That evolution is natural, said planning agency director Brian Golden, who notes the Seaport is still only half-built. “The Seaport’s ultimate evolution will be something completely different than it is today,’’ he said.

What, exactly, the Seaport becomes will likely be debated long after Thursday night’s vote. City Council President Michelle Wu had scheduled a hearing Thursday to examine the lack of public facilities in a neighborhood that could eventually be home to 20,000 people. She postponed it at the planning agency’s request, so it wouldn’t conflict with Thursday’s board meeting, but she hopes to reschedule soon. Seaport Square won’t be the end of the conversation, Wu said.

“This particular project highlighted an issue the neighborhood has been struggling with for a very long time,’’ said Wu, who noted that the Seaport has no fire stations.

Jon Chesto and Milton Valencia of the Globe Staff contributed to this report. Tim Logan can be reached at tim.logan@globe.com.